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How To Write A Literature Review - A Complete Guide

Table of Contents

A literature review is much more than just another section in your research paper. It forms the very foundation of your research. It is a formal piece of writing where you analyze the existing theoretical framework, principles, and assumptions and use that as a base to shape your approach to the research question.

Curating and drafting a solid literature review section not only lends more credibility to your research paper but also makes your research tighter and better focused. But, writing literature reviews is a difficult task. It requires extensive reading, plus you have to consider market trends and technological and political changes, which tend to change in the blink of an eye.

Now streamline your literature review process with the help of SciSpace Copilot. With this AI research assistant, you can efficiently synthesize and analyze a vast amount of information, identify key themes and trends, and uncover gaps in the existing research. Get real-time explanations, summaries, and answers to your questions for the paper you're reviewing, making navigating and understanding the complex literature landscape easier.

In this comprehensive guide, we will explore everything from the definition of a literature review, its appropriate length, various types of literature reviews, and how to write one.

What is a literature review?

A literature review is a collation of survey, research, critical evaluation, and assessment of the existing literature in a preferred domain.

Eminent researcher and academic Arlene Fink, in her book Conducting Research Literature Reviews , defines it as the following:

“A literature review surveys books, scholarly articles, and any other sources relevant to a particular issue, area of research, or theory, and by so doing, provides a description, summary, and critical evaluation of these works in relation to the research problem being investigated.

Literature reviews are designed to provide an overview of sources you have explored while researching a particular topic, and to demonstrate to your readers how your research fits within a larger field of study.”

Simply put, a literature review can be defined as a critical discussion of relevant pre-existing research around your research question and carving out a definitive place for your study in the existing body of knowledge. Literature reviews can be presented in multiple ways: a section of an article, the whole research paper itself, or a chapter of your thesis.

A literature review does function as a summary of sources, but it also allows you to analyze further, interpret, and examine the stated theories, methods, viewpoints, and, of course, the gaps in the existing content.

As an author, you can discuss and interpret the research question and its various aspects and debate your adopted methods to support the claim.

What is the purpose of a literature review?

A literature review is meant to help your readers understand the relevance of your research question and where it fits within the existing body of knowledge. As a researcher, you should use it to set the context, build your argument, and establish the need for your study.

What is the importance of a literature review?

The literature review is a critical part of research papers because it helps you:

• Gain an in-depth understanding of your research question and the surrounding area
• Convey that you have a thorough understanding of your research area and are up-to-date with the latest changes and advancements
• Establish how your research is connected or builds on the existing body of knowledge and how it could contribute to further research
• Elaborate on the validity and suitability of your theoretical framework and research methodology
• Identify and highlight gaps and shortcomings in the existing body of knowledge and how things need to change
• Convey to readers how your study is different or how it contributes to the research area

How long should a literature review be?

Ideally, the literature review should take up 15%-40% of the total length of your manuscript. So, if you have a 10,000-word research paper, the minimum word count could be 1500.

Your literature review format depends heavily on the kind of manuscript you are writing — an entire chapter in case of doctoral theses, a part of the introductory section in a research article, to a full-fledged review article that examines the previously published research on a topic.

Another determining factor is the type of research you are doing. The literature review section tends to be longer for secondary research projects than primary research projects.

What are the different types of literature reviews?

All literature reviews are not the same. There are a variety of possible approaches that you can take. It all depends on the type of research you are pursuing.

Here are the different types of literature reviews:

Argumentative review

It is called an argumentative review when you carefully present literature that only supports or counters a specific argument or premise to establish a viewpoint.

Integrative review

It is a type of literature review focused on building a comprehensive understanding of a topic by combining available theoretical frameworks and empirical evidence.

Methodological review

This approach delves into the ''how'' and the ''what" of the research question —  you cannot look at the outcome in isolation; you should also review the methodology used.

Systematic review

This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research and collect, report, and analyze data from the studies included in the review.

Meta-analysis review

Meta-analysis uses statistical methods to summarize the results of independent studies. By combining information from all relevant studies, meta-analysis can provide more precise estimates of the effects than those derived from the individual studies included within a review.

Historical review

Historical literature reviews focus on examining research throughout a period, often starting with the first time an issue, concept, theory, or phenomenon emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and identify future research's likely directions.

Theoretical Review

This form aims to examine the corpus of theory accumulated regarding an issue, concept, theory, and phenomenon. The theoretical literature review helps to establish what theories exist, the relationships between them, the degree the existing approaches have been investigated, and to develop new hypotheses to be tested.

Scoping Review

The Scoping Review is often used at the beginning of an article, dissertation, or research proposal. It is conducted before the research to highlight gaps in the existing body of knowledge and explains why the project should be greenlit.

State-of-the-Art Review

The State-of-the-Art review is conducted periodically, focusing on the most recent research. It describes what is currently known, understood, or agreed upon regarding the research topic and highlights where there are still disagreements.

Can you use the first person in a literature review?

When writing literature reviews, you should avoid the usage of first-person pronouns. It means that instead of "I argue that" or "we argue that," the appropriate expression would be "this research paper argues that."

Do you need an abstract for a literature review?

Ideally, yes. It is always good to have a condensed summary that is self-contained and independent of the rest of your review. As for how to draft one, you can follow the same fundamental idea when preparing an abstract for a literature review. It should also include:

• The research topic and your motivation behind selecting it
• A one-sentence thesis statement
• An explanation of the kinds of literature featured in the review
• Summary of what you've learned
• Conclusions you drew from the literature you reviewed
• Potential implications and future scope for research

Here's an example of the abstract of a literature review

Is a literature review written in the past tense?

Yes, the literature review should ideally be written in the past tense. You should not use the present or future tense when writing one. The exceptions are when you have statements describing events that happened earlier than the literature you are reviewing or events that are currently occurring; then, you can use the past perfect or present perfect tenses.

How many sources for a literature review?

There are multiple approaches to deciding how many sources to include in a literature review section. The first approach would be to look level you are at as a researcher. For instance, a doctoral thesis might need 60+ sources. In contrast, you might only need to refer to 5-15 sources at the undergraduate level.

The second approach is based on the kind of literature review you are doing — whether it is merely a chapter of your paper or if it is a self-contained paper in itself. When it is just a chapter, sources should equal the total number of pages in your article's body. In the second scenario, you need at least three times as many sources as there are pages in your work.

Quick tips on how to write a literature review

To know how to write a literature review, you must clearly understand its impact and role in establishing your work as substantive research material.

You need to follow the below-mentioned steps, to write a literature review:

• Outline the purpose behind the literature review
• Search relevant literature
• Examine and assess the relevant resources
• Discover connections by drawing deep insights from the resources
• Structure planning to write a good literature review

1. Outline and identify the purpose of  a literature review

As a first step on how to write a literature review, you must know what the research question or topic is and what shape you want your literature review to take. Ensure you understand the research topic inside out, or else seek clarifications. You must be able to the answer below questions before you start:

• How many sources do I need to include?
• What kind of sources should I analyze?
• How much should I critically evaluate each source?
• Should I summarize, synthesize or offer a critique of the sources?
• Do I need to include any background information or definitions?

Additionally, you should know that the narrower your research topic is, the swifter it will be for you to restrict the number of sources to be analyzed.

2. Search relevant literature

Dig deeper into search engines to discover what has already been published around your chosen topic. Make sure you thoroughly go through appropriate reference sources like books, reports, journal articles, government docs, and web-based resources.

You must prepare a list of keywords and their different variations. You can start your search from any library’s catalog, provided you are an active member of that institution. The exact keywords can be extended to widen your research over other databases and academic search engines like:

• Google Scholar
• Microsoft Academic
• Science.gov

Besides, it is not advisable to go through every resource word by word. Alternatively, what you can do is you can start by reading the abstract and then decide whether that source is relevant to your research or not.

Additionally, you must spend surplus time assessing the quality and relevance of resources. It would help if you tried preparing a list of citations to ensure that there lies no repetition of authors, publications, or articles in the literature review.

3. Examine and assess the sources

It is nearly impossible for you to go through every detail in the research article. So rather than trying to fetch every detail, you have to analyze and decide which research sources resemble closest and appear relevant to your chosen domain.

While analyzing the sources, you should look to find out answers to questions like:

• What question or problem has the author been describing and debating?
• What is the definition of critical aspects?
• How well the theories, approach, and methodology have been explained?
• Whether the research theory used some conventional or new innovative approach?
• How relevant are the key findings of the work?
• In what ways does it relate to other sources on the same topic?
• What challenges does this research paper pose to the existing theory
• What are the possible contributions or benefits it adds to the subject domain?

Be always mindful that you refer only to credible and authentic resources. It would be best if you always take references from different publications to validate your theory.

Always keep track of important information or data you can present in your literature review right from the beginning. It will help steer your path from any threats of plagiarism and also make it easier to curate an annotated bibliography or reference section.

4. Discover connections

At this stage, you must start deciding on the argument and structure of your literature review. To accomplish this, you must discover and identify the relations and connections between various resources while drafting your abstract.

A few aspects that you should be aware of while writing a literature review include:

• Rise to prominence: Theories and methods that have gained reputation and supporters over time.
• Constant scrutiny: Concepts or theories that repeatedly went under examination.
• Contradictions and conflicts: Theories, both the supporting and the contradictory ones, for the research topic.
• Knowledge gaps: What exactly does it fail to address, and how to bridge them with further research?
• Influential resources: Significant research projects available that have been upheld as milestones or perhaps, something that can modify the current trends

Once you join the dots between various past research works, it will be easier for you to draw a conclusion and identify your contribution to the existing knowledge base.

5. Structure planning to write a good literature review

There exist different ways towards planning and executing the structure of a literature review. The format of a literature review varies and depends upon the length of the research.

Like any other research paper, the literature review format must contain three sections: introduction, body, and conclusion. The goals and objectives of the research question determine what goes inside these three sections.

Nevertheless, a good literature review can be structured according to the chronological, thematic, methodological, or theoretical framework approach.

Literature review samples

1. Standalone

2. As a section of a research paper

How SciSpace Discover makes literature review a breeze?

SciSpace Discover is a one-stop solution to do an effective literature search and get barrier-free access to scientific knowledge. It is an excellent repository where you can find millions of only peer-reviewed articles and full-text PDF files. Here’s more on how you can use it:

Find the right information

Find what you want quickly and easily with comprehensive search filters that let you narrow down papers according to PDF availability, year of publishing, document type, and affiliated institution. Moreover, you can sort the results based on the publishing date, citation count, and relevance.

Assess credibility of papers quickly

When doing the literature review, it is critical to establish the quality of your sources. They form the foundation of your research. SciSpace Discover helps you assess the quality of a source by providing an overview of its references, citations, and performance metrics.

Get the complete picture in no time

SciSpace Discover’s personalized suggestion engine helps you stay on course and get the complete picture of the topic from one place. Every time you visit an article page, it provides you links to related papers. Besides that, it helps you understand what’s trending, who are the top authors, and who are the leading publishers on a topic.

Make referring sources super easy

To ensure you don't lose track of your sources, you must start noting down your references when doing the literature review. SciSpace Discover makes this step effortless. Click the 'cite' button on an article page, and you will receive preloaded citation text in multiple styles — all you've to do is copy-paste it into your manuscript.

Final tips on how to write a literature review

A massive chunk of time and effort is required to write a good literature review. But, if you go about it systematically, you'll be able to save a ton of time and build a solid foundation for your research.

We hope this guide has helped you answer several key questions you have about writing literature reviews.

Would you like to explore SciSpace Discover and kick off your literature search right away? You can get started here .

Frequently Asked Questions (FAQs)

1. how to start a literature review.

• What questions do you want to answer?

• What sources do you need to answer these questions?

• What information do these sources contain?

• How can you use this information to answer your questions?

2. What to include in a literature review?

• A brief background of the problem or issue

• What has previously been done to address the problem or issue

• A description of what you will do in your project

• How this study will contribute to research on the subject

3. Why literature review is important?

The literature review is an important part of any research project because it allows the writer to look at previous studies on a topic and determine existing gaps in the literature, as well as what has already been done. It will also help them to choose the most appropriate method for their own study.

4. How to cite a literature review in APA format?

To cite a literature review in APA style, you need to provide the author's name, the title of the article, and the year of publication. For example: Patel, A. B., & Stokes, G. S. (2012). The relationship between personality and intelligence: A meta-analysis of longitudinal research. Personality and Individual Differences, 53(1), 16-21

5. What are the components of a literature review?

• A brief introduction to the topic, including its background and context. The introduction should also include a rationale for why the study is being conducted and what it will accomplish.

• A description of the methodologies used in the study. This can include information about data collection methods, sample size, and statistical analyses.

• A presentation of the findings in an organized format that helps readers follow along with the author's conclusions.

6. What are common errors in writing literature review?

• Not spending enough time to critically evaluate the relevance of resources, observations and conclusions.

• Totally relying on secondary data while ignoring primary data.

• Letting your personal bias seep into your interpretation of existing literature.

• No detailed explanation of the procedure to discover and identify an appropriate literature review.

7. What are the 5 C's of writing literature review?

• Cite - the sources you utilized and referenced in your research.

• Compare - existing arguments, hypotheses, methodologies, and conclusions found in the knowledge base.

• Contrast - the arguments, topics, methodologies, approaches, and disputes that may be found in the literature.

• Critique - the literature and describe the ideas and opinions you find more convincing and why.

• Connect - the various studies you reviewed in your research.

8. How many sources should a literature review have?

When it is just a chapter, sources should equal the total number of pages in your article's body. if it is a self-contained paper in itself, you need at least three times as many sources as there are pages in your work.

9. Can literature review have diagrams?

• To represent an abstract idea or concept

• To explain the steps of a process or procedure

• To help readers understand the relationships between different concepts

10. How old should sources be in a literature review?

Sources for a literature review should be as current as possible or not older than ten years. The only exception to this rule is if you are reviewing a historical topic and need to use older sources.

11. What are the types of literature review?

• Argumentative review

• Integrative review

• Methodological review

• Systematic review

• Meta-analysis review

• Historical review

• Theoretical review

• Scoping review

• State-of-the-Art review

12. Is a literature review mandatory?

Yes. Literature review is a mandatory part of any research project. It is a critical step in the process that allows you to establish the scope of your research, and provide a background for the rest of your work.

But before you go,

• Six Online Tools for Easy Literature Review
• Evaluating literature review: systematic vs. scoping reviews
• Systematic Approaches to a Successful Literature Review
• Writing Integrative Literature Reviews: Guidelines and Examples

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• What is a Literature Review? | Guide, Template, & Examples

What is a Literature Review? | Guide, Template, & Examples

Published on 22 February 2022 by Shona McCombes . Revised on 7 June 2022.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research.

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarise sources – it analyses, synthesises, and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

Why write a literature review, examples of literature reviews, step 1: search for relevant literature, step 2: evaluate and select sources, step 3: identify themes, debates and gaps, step 4: outline your literature review’s structure, step 5: write your literature review, frequently asked questions about literature reviews, introduction.

• Quick Run-through
• Step 1 & 2

When you write a dissertation or thesis, you will have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and scholarly context
• Develop a theoretical framework and methodology for your research
• Position yourself in relation to other researchers and theorists
• Show how your dissertation addresses a gap or contributes to a debate

You might also have to write a literature review as a stand-alone assignment. In this case, the purpose is to evaluate the current state of research and demonstrate your knowledge of scholarly debates around a topic.

The content will look slightly different in each case, but the process of conducting a literature review follows the same steps. We’ve written a step-by-step guide that you can follow below.

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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research objectives and questions .

If you are writing a literature review as a stand-alone assignment, you will have to choose a focus and develop a central question to direct your search. Unlike a dissertation research question, this question has to be answerable without collecting original data. You should be able to answer it based only on a review of existing publications.

Make a list of keywords

Start by creating a list of keywords related to your research topic. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list if you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can use boolean operators to help narrow down your search:

Read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

To identify the most important publications on your topic, take note of recurring citations. If the same authors, books or articles keep appearing in your reading, make sure to seek them out.

You probably won’t be able to read absolutely everything that has been written on the topic – you’ll have to evaluate which sources are most relevant to your questions.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models and methods? Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• How does the publication contribute to your understanding of the topic? What are its key insights and arguments?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible, and make sure you read any landmark studies and major theories in your field of research.

You can find out how many times an article has been cited on Google Scholar – a high citation count means the article has been influential in the field, and should certainly be included in your literature review.

The scope of your review will depend on your topic and discipline: in the sciences you usually only review recent literature, but in the humanities you might take a long historical perspective (for example, to trace how a concept has changed in meaning over time).

Remember that you can use our template to summarise and evaluate sources you’re thinking about using!

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It’s important to keep track of your sources with references to avoid plagiarism . It can be helpful to make an annotated bibliography, where you compile full reference information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

You can use our free APA Reference Generator for quick, correct, consistent citations.

To begin organising your literature review’s argument and structure, you need to understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly-visual platforms like Instagram and Snapchat – this is a gap that you could address in your own research.

There are various approaches to organising the body of a literature review. You should have a rough idea of your strategy before you start writing.

Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarising sources in order.

Try to analyse patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organise your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text, your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

If you are writing the literature review as part of your dissertation or thesis, reiterate your central problem or research question and give a brief summary of the scholarly context. You can emphasise the timeliness of the topic (“many recent studies have focused on the problem of x”) or highlight a gap in the literature (“while there has been much research on x, few researchers have taken y into consideration”).

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, make sure to follow these tips:

• Summarise and synthesise: give an overview of the main points of each source and combine them into a coherent whole.
• Analyse and interpret: don’t just paraphrase other researchers – add your own interpretations, discussing the significance of findings in relation to the literature as a whole.
• Critically evaluate: mention the strengths and weaknesses of your sources.
• Write in well-structured paragraphs: use transitions and topic sentences to draw connections, comparisons and contrasts.

In the conclusion, you should summarise the key findings you have taken from the literature and emphasise their significance.

If the literature review is part of your dissertation or thesis, reiterate how your research addresses gaps and contributes new knowledge, or discuss how you have drawn on existing theories and methods to build a framework for your research. This can lead directly into your methodology section.

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a dissertation , thesis, research paper , or proposal .

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarise yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your  dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

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Research Methods

• Getting Started
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Literature Review

• What is a Literature Review?
• What is NOT a Literature Review?
• Purposes of a Literature Review
• Types of Literature Reviews
• Literature Reviews vs. Systematic Reviews
• Systematic vs. Meta-Analysis

Literature Review  is a comprehensive survey of the works published in a particular field of study or line of research, usually over a specific period of time, in the form of an in-depth, critical bibliographic essay or annotated list in which attention is drawn to the most significant works.

Also, we can define a literature review as the collected body of scholarly works related to a topic:

• Summarizes and analyzes previous research relevant to a topic
• Includes scholarly books and articles published in academic journals
• Can be an specific scholarly paper or a section in a research paper

The objective of a Literature Review is to find previous published scholarly works relevant to an specific topic

• Help gather ideas or information
• Keep up to date in current trends and findings
• Help develop new questions

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Helps focus your own research questions or problems
• Discovers relationships between research studies/ideas.
• Suggests unexplored ideas or populations
• Identifies major themes, concepts, and researchers on a topic.
• Tests assumptions; may help counter preconceived ideas and remove unconscious bias.
• Identifies critical gaps, points of disagreement, or potentially flawed methodology or theoretical approaches.
• Indicates potential directions for future research.

All content in this section is from Literature Review Research from Old Dominion University 

Keep in mind the following, a literature review is NOT:

Not an essay 

Not an annotated bibliography  in which you summarize each article that you have reviewed.  A literature review goes beyond basic summarizing to focus on the critical analysis of the reviewed works and their relationship to your research question.

Not a research paper   where you select resources to support one side of an issue versus another.  A lit review should explain and consider all sides of an argument in order to avoid bias, and areas of agreement and disagreement should be highlighted.

A literature review serves several purposes. For example, it

• provides thorough knowledge of previous studies; introduces seminal works.
• helps focus one’s own research topic.
• identifies a conceptual framework for one’s own research questions or problems; indicates potential directions for future research.
• suggests previously unused or underused methodologies, designs, quantitative and qualitative strategies.
• identifies gaps in previous studies; identifies flawed methodologies and/or theoretical approaches; avoids replication of mistakes.
• helps the researcher avoid repetition of earlier research.
• suggests unexplored populations.
• determines whether past studies agree or disagree; identifies controversy in the literature.
• tests assumptions; may help counter preconceived ideas and remove unconscious bias.

As Kennedy (2007) notes*, it is important to think of knowledge in a given field as consisting of three layers. First, there are the primary studies that researchers conduct and publish. Second are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the original studies. Third, there are the perceptions, conclusions, opinion, and interpretations that are shared informally that become part of the lore of field. In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews.

Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are several approaches to how they can be done, depending upon the type of analysis underpinning your study. Listed below are definitions of types of literature reviews:

Argumentative Review      This form examines literature selectively in order to support or refute an argument, deeply imbedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to to make summary claims of the sort found in systematic reviews.

Integrative Review      Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication.

Historical Review      Few things rest in isolation from historical precedent. Historical reviews are focused on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.

Methodological Review      A review does not always focus on what someone said [content], but how they said it [method of analysis]. This approach provides a framework of understanding at different levels (i.e. those of theory, substantive fields, research approaches and data collection and analysis techniques), enables researchers to draw on a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection and data analysis, and helps highlight many ethical issues which we should be aware of and consider as we go through our study.

Systematic Review      This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyse data from the studies that are included in the review. Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?"

Theoretical Review      The purpose of this form is to concretely examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomena. The theoretical literature review help establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.

* Kennedy, Mary M. "Defining a Literature."  Educational Researcher  36 (April 2007): 139-147.

All content in this section is from The Literature Review created by Dr. Robert Larabee USC

Robinson, P. and Lowe, J. (2015),  Literature reviews vs systematic reviews.  Australian and New Zealand Journal of Public Health, 39: 103-103. doi: 10.1111/1753-6405.12393

What's in the name? The difference between a Systematic Review and a Literature Review, and why it matters . By Lynn Kysh from University of Southern California

Systematic review or meta-analysis?

A  systematic review  answers a defined research question by collecting and summarizing all empirical evidence that fits pre-specified eligibility criteria.

A  meta-analysis  is the use of statistical methods to summarize the results of these studies.

Systematic reviews, just like other research articles, can be of varying quality. They are a significant piece of work (the Centre for Reviews and Dissemination at York estimates that a team will take 9-24 months), and to be useful to other researchers and practitioners they should have:

• clearly stated objectives with pre-defined eligibility criteria for studies
• explicit, reproducible methodology
• a systematic search that attempts to identify all studies
• assessment of the validity of the findings of the included studies (e.g. risk of bias)
• systematic presentation, and synthesis, of the characteristics and findings of the included studies

Not all systematic reviews contain meta-analysis. 

Meta-analysis is the use of statistical methods to summarize the results of independent studies. By combining information from all relevant studies, meta-analysis can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review.  More information on meta-analyses can be found in  Cochrane Handbook, Chapter 9 .

A meta-analysis goes beyond critique and integration and conducts secondary statistical analysis on the outcomes of similar studies.  It is a systematic review that uses quantitative methods to synthesize and summarize the results.

An advantage of a meta-analysis is the ability to be completely objective in evaluating research findings.  Not all topics, however, have sufficient research evidence to allow a meta-analysis to be conducted.  In that case, an integrative review is an appropriate strategy. 

Some of the content in this section is from Systematic reviews and meta-analyses: step by step guide created by Kate McAllister.

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Organizing Your Social Sciences Research Paper

• 5. The Literature Review
• Purpose of Guide
• Design Flaws to Avoid
• Independent and Dependent Variables
• Glossary of Research Terms
• Reading Research Effectively
• Narrowing a Topic Idea
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• Theoretical Framework
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A literature review surveys prior research published in books, scholarly articles, and any other sources relevant to a particular issue, area of research, or theory, and by so doing, provides a description, summary, and critical evaluation of these works in relation to the research problem being investigated. Literature reviews are designed to provide an overview of sources you have used in researching a particular topic and to demonstrate to your readers how your research fits within existing scholarship about the topic.

Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . Fourth edition. Thousand Oaks, CA: SAGE, 2014.

Importance of a Good Literature Review

A literature review may consist of simply a summary of key sources, but in the social sciences, a literature review usually has an organizational pattern and combines both summary and synthesis, often within specific conceptual categories . A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information in a way that informs how you are planning to investigate a research problem. The analytical features of a literature review might:

• Give a new interpretation of old material or combine new with old interpretations,
• Trace the intellectual progression of the field, including major debates,
• Depending on the situation, evaluate the sources and advise the reader on the most pertinent or relevant research, or
• Usually in the conclusion of a literature review, identify where gaps exist in how a problem has been researched to date.

Given this, the purpose of a literature review is to:

• Place each work in the context of its contribution to understanding the research problem being studied.
• Describe the relationship of each work to the others under consideration.
• Identify new ways to interpret prior research.
• Reveal any gaps that exist in the literature.
• Resolve conflicts amongst seemingly contradictory previous studies.
• Identify areas of prior scholarship to prevent duplication of effort.
• Point the way in fulfilling a need for additional research.
• Locate your own research within the context of existing literature [very important].

Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper. 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . Los Angeles, CA: SAGE, 2011; Knopf, Jeffrey W. "Doing a Literature Review." PS: Political Science and Politics 39 (January 2006): 127-132; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012.

Types of Literature Reviews

It is important to think of knowledge in a given field as consisting of three layers. First, there are the primary studies that researchers conduct and publish. Second are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the primary studies. Third, there are the perceptions, conclusions, opinion, and interpretations that are shared informally among scholars that become part of the body of epistemological traditions within the field.

In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews. Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are a number of approaches you could adopt depending upon the type of analysis underpinning your study.

Argumentative Review This form examines literature selectively in order to support or refute an argument, deeply embedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to make summary claims of the sort found in systematic reviews [see below].

Integrative Review Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses or research problems. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication. This is the most common form of review in the social sciences.

Historical Review Few things rest in isolation from historical precedent. Historical literature reviews focus on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.

Methodological Review A review does not always focus on what someone said [findings], but how they came about saying what they say [method of analysis]. Reviewing methods of analysis provides a framework of understanding at different levels [i.e. those of theory, substantive fields, research approaches, and data collection and analysis techniques], how researchers draw upon a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection, and data analysis. This approach helps highlight ethical issues which you should be aware of and consider as you go through your own study.

Systematic Review This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyze data from the studies that are included in the review. The goal is to deliberately document, critically evaluate, and summarize scientifically all of the research about a clearly defined research problem . Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?" This type of literature review is primarily applied to examining prior research studies in clinical medicine and allied health fields, but it is increasingly being used in the social sciences.

Theoretical Review The purpose of this form is to examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomena. The theoretical literature review helps to establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.

NOTE : Most often the literature review will incorporate some combination of types. For example, a review that examines literature supporting or refuting an argument, assumption, or philosophical problem related to the research problem will also need to include writing supported by sources that establish the history of these arguments in the literature.

Baumeister, Roy F. and Mark R. Leary. "Writing Narrative Literature Reviews."  Review of General Psychology 1 (September 1997): 311-320; Mark R. Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Kennedy, Mary M. "Defining a Literature." Educational Researcher 36 (April 2007): 139-147; Petticrew, Mark and Helen Roberts. Systematic Reviews in the Social Sciences: A Practical Guide . Malden, MA: Blackwell Publishers, 2006; Torracro, Richard. "Writing Integrative Literature Reviews: Guidelines and Examples." Human Resource Development Review 4 (September 2005): 356-367; Rocco, Tonette S. and Maria S. Plakhotnik. "Literature Reviews, Conceptual Frameworks, and Theoretical Frameworks: Terms, Functions, and Distinctions." Human Ressource Development Review 8 (March 2008): 120-130; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.

Structure and Writing Style

I.  Thinking About Your Literature Review

The structure of a literature review should include the following in support of understanding the research problem :

• An overview of the subject, issue, or theory under consideration, along with the objectives of the literature review,
• Division of works under review into themes or categories [e.g. works that support a particular position, those against, and those offering alternative approaches entirely],
• An explanation of how each work is similar to and how it varies from the others,
• Conclusions as to which pieces are best considered in their argument, are most convincing of their opinions, and make the greatest contribution to the understanding and development of their area of research.

The critical evaluation of each work should consider :

• Provenance -- what are the author's credentials? Are the author's arguments supported by evidence [e.g. primary historical material, case studies, narratives, statistics, recent scientific findings]?
• Methodology -- were the techniques used to identify, gather, and analyze the data appropriate to addressing the research problem? Was the sample size appropriate? Were the results effectively interpreted and reported?
• Objectivity -- is the author's perspective even-handed or prejudicial? Is contrary data considered or is certain pertinent information ignored to prove the author's point?
• Persuasiveness -- which of the author's theses are most convincing or least convincing?
• Validity -- are the author's arguments and conclusions convincing? Does the work ultimately contribute in any significant way to an understanding of the subject?

II.  Development of the Literature Review

Four Basic Stages of Writing 1.  Problem formulation -- which topic or field is being examined and what are its component issues? 2.  Literature search -- finding materials relevant to the subject being explored. 3.  Data evaluation -- determining which literature makes a significant contribution to the understanding of the topic. 4.  Analysis and interpretation -- discussing the findings and conclusions of pertinent literature.

Consider the following issues before writing the literature review: Clarify If your assignment is not specific about what form your literature review should take, seek clarification from your professor by asking these questions: 1.  Roughly how many sources would be appropriate to include? 2.  What types of sources should I review (books, journal articles, websites; scholarly versus popular sources)? 3.  Should I summarize, synthesize, or critique sources by discussing a common theme or issue? 4.  Should I evaluate the sources in any way beyond evaluating how they relate to understanding the research problem? 5.  Should I provide subheadings and other background information, such as definitions and/or a history? Find Models Use the exercise of reviewing the literature to examine how authors in your discipline or area of interest have composed their literature review sections. Read them to get a sense of the types of themes you might want to look for in your own research or to identify ways to organize your final review. The bibliography or reference section of sources you've already read, such as required readings in the course syllabus, are also excellent entry points into your own research. Narrow the Topic The narrower your topic, the easier it will be to limit the number of sources you need to read in order to obtain a good survey of relevant resources. Your professor will probably not expect you to read everything that's available about the topic, but you'll make the act of reviewing easier if you first limit scope of the research problem. A good strategy is to begin by searching the USC Libraries Catalog for recent books about the topic and review the table of contents for chapters that focuses on specific issues. You can also review the indexes of books to find references to specific issues that can serve as the focus of your research. For example, a book surveying the history of the Israeli-Palestinian conflict may include a chapter on the role Egypt has played in mediating the conflict, or look in the index for the pages where Egypt is mentioned in the text. Consider Whether Your Sources are Current Some disciplines require that you use information that is as current as possible. This is particularly true in disciplines in medicine and the sciences where research conducted becomes obsolete very quickly as new discoveries are made. However, when writing a review in the social sciences, a survey of the history of the literature may be required. In other words, a complete understanding the research problem requires you to deliberately examine how knowledge and perspectives have changed over time. Sort through other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to explore what is considered by scholars to be a "hot topic" and what is not.

III.  Ways to Organize Your Literature Review

Chronology of Events If your review follows the chronological method, you could write about the materials according to when they were published. This approach should only be followed if a clear path of research building on previous research can be identified and that these trends follow a clear chronological order of development. For example, a literature review that focuses on continuing research about the emergence of German economic power after the fall of the Soviet Union. By Publication Order your sources by publication chronology, then, only if the order demonstrates a more important trend. For instance, you could order a review of literature on environmental studies of brown fields if the progression revealed, for example, a change in the soil collection practices of the researchers who wrote and/or conducted the studies. Thematic [“conceptual categories”] A thematic literature review is the most common approach to summarizing prior research in the social and behavioral sciences. Thematic reviews are organized around a topic or issue, rather than the progression of time, although the progression of time may still be incorporated into a thematic review. For example, a review of the Internet’s impact on American presidential politics could focus on the development of online political satire. While the study focuses on one topic, the Internet’s impact on American presidential politics, it would still be organized chronologically reflecting technological developments in media. The difference in this example between a "chronological" and a "thematic" approach is what is emphasized the most: themes related to the role of the Internet in presidential politics. Note that more authentic thematic reviews tend to break away from chronological order. A review organized in this manner would shift between time periods within each section according to the point being made. Methodological A methodological approach focuses on the methods utilized by the researcher. For the Internet in American presidential politics project, one methodological approach would be to look at cultural differences between the portrayal of American presidents on American, British, and French websites. Or the review might focus on the fundraising impact of the Internet on a particular political party. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed.

Other Sections of Your Literature Review Once you've decided on the organizational method for your literature review, the sections you need to include in the paper should be easy to figure out because they arise from your organizational strategy. In other words, a chronological review would have subsections for each vital time period; a thematic review would have subtopics based upon factors that relate to the theme or issue. However, sometimes you may need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. However, only include what is necessary for the reader to locate your study within the larger scholarship about the research problem.

Here are examples of other sections, usually in the form of a single paragraph, you may need to include depending on the type of review you write:

• Current Situation : Information necessary to understand the current topic or focus of the literature review.
• Sources Used : Describes the methods and resources [e.g., databases] you used to identify the literature you reviewed.
• History : The chronological progression of the field, the research literature, or an idea that is necessary to understand the literature review, if the body of the literature review is not already a chronology.
• Selection Methods : Criteria you used to select (and perhaps exclude) sources in your literature review. For instance, you might explain that your review includes only peer-reviewed [i.e., scholarly] sources.
• Standards : Description of the way in which you present your information.
• Questions for Further Research : What questions about the field has the review sparked? How will you further your research as a result of the review?

IV.  Writing Your Literature Review

Once you've settled on how to organize your literature review, you're ready to write each section. When writing your review, keep in mind these issues.

Use Evidence A literature review section is, in this sense, just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence [citations] that demonstrates that what you are saying is valid. Be Selective Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the research problem, whether it is thematic, methodological, or chronological. Related items that provide additional information, but that are not key to understanding the research problem, can be included in a list of further readings . Use Quotes Sparingly Some short quotes are appropriate if you want to emphasize a point, or if what an author stated cannot be easily paraphrased. Sometimes you may need to quote certain terminology that was coined by the author, is not common knowledge, or taken directly from the study. Do not use extensive quotes as a substitute for using your own words in reviewing the literature. Summarize and Synthesize Remember to summarize and synthesize your sources within each thematic paragraph as well as throughout the review. Recapitulate important features of a research study, but then synthesize it by rephrasing the study's significance and relating it to your own work and the work of others. Keep Your Own Voice While the literature review presents others' ideas, your voice [the writer's] should remain front and center. For example, weave references to other sources into what you are writing but maintain your own voice by starting and ending the paragraph with your own ideas and wording. Use Caution When Paraphrasing When paraphrasing a source that is not your own, be sure to represent the author's information or opinions accurately and in your own words. Even when paraphrasing an author’s work, you still must provide a citation to that work.

V.  Common Mistakes to Avoid

These are the most common mistakes made in reviewing social science research literature.

• Sources in your literature review do not clearly relate to the research problem;
• You do not take sufficient time to define and identify the most relevant sources to use in the literature review related to the research problem;
• Relies exclusively on secondary analytical sources rather than including relevant primary research studies or data;
• Uncritically accepts another researcher's findings and interpretations as valid, rather than examining critically all aspects of the research design and analysis;
• Does not describe the search procedures that were used in identifying the literature to review;
• Reports isolated statistical results rather than synthesizing them in chi-squared or meta-analytic methods; and,
• Only includes research that validates assumptions and does not consider contrary findings and alternative interpretations found in the literature.

Cook, Kathleen E. and Elise Murowchick. “Do Literature Review Skills Transfer from One Course to Another?” Psychology Learning and Teaching 13 (March 2014): 3-11; Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . London: SAGE, 2011; Literature Review Handout. Online Writing Center. Liberty University; Literature Reviews. The Writing Center. University of North Carolina; Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: SAGE, 2016; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012; Randolph, Justus J. “A Guide to Writing the Dissertation Literature Review." Practical Assessment, Research, and Evaluation. vol. 14, June 2009; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016; Taylor, Dena. The Literature Review: A Few Tips On Conducting It. University College Writing Centre. University of Toronto; Writing a Literature Review. Academic Skills Centre. University of Canberra.

Writing Tip

Break Out of Your Disciplinary Box!

Thinking interdisciplinarily about a research problem can be a rewarding exercise in applying new ideas, theories, or concepts to an old problem. For example, what might cultural anthropologists say about the continuing conflict in the Middle East? In what ways might geographers view the need for better distribution of social service agencies in large cities than how social workers might study the issue? You don’t want to substitute a thorough review of core research literature in your discipline for studies conducted in other fields of study. However, particularly in the social sciences, thinking about research problems from multiple vectors is a key strategy for finding new solutions to a problem or gaining a new perspective. Consult with a librarian about identifying research databases in other disciplines; almost every field of study has at least one comprehensive database devoted to indexing its research literature.

Frodeman, Robert. The Oxford Handbook of Interdisciplinarity . New York: Oxford University Press, 2010.

Another Writing Tip

Don't Just Review for Content!

While conducting a review of the literature, maximize the time you devote to writing this part of your paper by thinking broadly about what you should be looking for and evaluating. Review not just what scholars are saying, but how are they saying it. Some questions to ask:

• How are they organizing their ideas?
• What methods have they used to study the problem?
• What theories have been used to explain, predict, or understand their research problem?
• What sources have they cited to support their conclusions?
• How have they used non-textual elements [e.g., charts, graphs, figures, etc.] to illustrate key points?

When you begin to write your literature review section, you'll be glad you dug deeper into how the research was designed and constructed because it establishes a means for developing more substantial analysis and interpretation of the research problem.

Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1 998.

Yet Another Writing Tip

When Do I Know I Can Stop Looking and Move On?

Here are several strategies you can utilize to assess whether you've thoroughly reviewed the literature:

• Look for repeating patterns in the research findings . If the same thing is being said, just by different people, then this likely demonstrates that the research problem has hit a conceptual dead end. At this point consider: Does your study extend current research?  Does it forge a new path? Or, does is merely add more of the same thing being said?
• Look at sources the authors cite to in their work . If you begin to see the same researchers cited again and again, then this is often an indication that no new ideas have been generated to address the research problem.
• Search Google Scholar to identify who has subsequently cited leading scholars already identified in your literature review [see next sub-tab]. This is called citation tracking and there are a number of sources that can help you identify who has cited whom, particularly scholars from outside of your discipline. Here again, if the same authors are being cited again and again, this may indicate no new literature has been written on the topic.

Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: Sage, 2016; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.

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How To Write An A-Grade Literature Review

3 straightforward steps (with examples) + free template.

By: Derek Jansen (MBA) | Expert Reviewed By: Dr. Eunice Rautenbach | October 2019

Quality research is about building onto the existing work of others , “standing on the shoulders of giants”, as Newton put it. The literature review chapter of your dissertation, thesis or research project is where you synthesise this prior work and lay the theoretical foundation for your own research.

Long story short, this chapter is a pretty big deal, which is why you want to make sure you get it right . In this post, I’ll show you exactly how to write a literature review in three straightforward steps, so you can conquer this vital chapter (the smart way).

Overview: The Literature Review Process

• Understanding the “ why “
• Finding the relevant literature
• Cataloguing and synthesising the information
• Outlining & writing up your literature review
• Example of a literature review

But first, the “why”…

Before we unpack how to write the literature review chapter, we’ve got to look at the why . To put it bluntly, if you don’t understand the function and purpose of the literature review process, there’s no way you can pull it off well. So, what exactly is the purpose of the literature review?

Well, there are (at least) four core functions:

• For you to gain an understanding (and demonstrate this understanding) of where the research is at currently, what the key arguments and disagreements are.
• For you to identify the gap(s) in the literature and then use this as justification for your own research topic.
• To help you build a conceptual framework for empirical testing (if applicable to your research topic).
• To inform your methodological choices and help you source tried and tested questionnaires (for interviews ) and measurement instruments (for surveys ).

Most students understand the first point but don’t give any thought to the rest. To get the most from the literature review process, you must keep all four points front of mind as you review the literature (more on this shortly), or you’ll land up with a wonky foundation.

Okay – with the why out the way, let’s move on to the how . As mentioned above, writing your literature review is a process, which I’ll break down into three steps:

• Finding the most suitable literature
• Understanding , distilling and organising the literature
• Planning and writing up your literature review chapter

Importantly, you must complete steps one and two before you start writing up your chapter. I know it’s very tempting, but don’t try to kill two birds with one stone and write as you read. You’ll invariably end up wasting huge amounts of time re-writing and re-shaping, or you’ll just land up with a disjointed, hard-to-digest mess . Instead, you need to read first and distil the information, then plan and execute the writing.

Step 1: Find the relevant literature

Naturally, the first step in the literature review journey is to hunt down the existing research that’s relevant to your topic. While you probably already have a decent base of this from your research proposal , you need to expand on this substantially in the dissertation or thesis itself.

Essentially, you need to be looking for any existing literature that potentially helps you answer your research question (or develop it, if that’s not yet pinned down). There are numerous ways to find relevant literature, but I’ll cover my top four tactics here. I’d suggest combining all four methods to ensure that nothing slips past you:

Method 1 – Google Scholar Scrubbing

Google’s academic search engine, Google Scholar , is a great starting point as it provides a good high-level view of the relevant journal articles for whatever keyword you throw at it. Most valuably, it tells you how many times each article has been cited, which gives you an idea of how credible (or at least, popular) it is. Some articles will be free to access, while others will require an account, which brings us to the next method.

Method 2 – University Database Scrounging

Generally, universities provide students with access to an online library, which provides access to many (but not all) of the major journals.

So, if you find an article using Google Scholar that requires paid access (which is quite likely), search for that article in your university’s database – if it’s listed there, you’ll have access. Note that, generally, the search engine capabilities of these databases are poor, so make sure you search for the exact article name, or you might not find it.

Method 3 – Journal Article Snowballing

At the end of every academic journal article, you’ll find a list of references. As with any academic writing, these references are the building blocks of the article, so if the article is relevant to your topic, there’s a good chance a portion of the referenced works will be too. Do a quick scan of the titles and see what seems relevant, then search for the relevant ones in your university’s database.

Method 4 – Dissertation Scavenging

Similar to Method 3 above, you can leverage other students’ dissertations. All you have to do is skim through literature review chapters of existing dissertations related to your topic and you’ll find a gold mine of potential literature. Usually, your university will provide you with access to previous students’ dissertations, but you can also find a much larger selection in the following databases:

• Open Access Theses & Dissertations
• Stanford SearchWorks

Keep in mind that dissertations and theses are not as academically sound as published, peer-reviewed journal articles (because they’re written by students, not professionals), so be sure to check the credibility of any sources you find using this method. You can do this by assessing the citation count of any given article in Google Scholar. If you need help with assessing the credibility of any article, or with finding relevant research in general, you can chat with one of our Research Specialists .

Alright – with a good base of literature firmly under your belt, it’s time to move onto the next step.

Need a helping hand?

Step 2: Log, catalogue and synthesise

Once you’ve built a little treasure trove of articles, it’s time to get reading and start digesting the information – what does it all mean?

While I present steps one and two (hunting and digesting) as sequential, in reality, it’s more of a back-and-forth tango – you’ll read a little , then have an idea, spot a new citation, or a new potential variable, and then go back to searching for articles. This is perfectly natural – through the reading process, your thoughts will develop , new avenues might crop up, and directional adjustments might arise. This is, after all, one of the main purposes of the literature review process (i.e. to familiarise yourself with the current state of research in your field).

As you’re working through your treasure chest, it’s essential that you simultaneously start organising the information. There are three aspects to this:

• Logging reference information
• Building an organised catalogue
• Distilling and synthesising the information

I’ll discuss each of these below:

2.1 – Log the reference information

As you read each article, you should add it to your reference management software. I usually recommend Mendeley for this purpose (see the Mendeley 101 video below), but you can use whichever software you’re comfortable with. Most importantly, make sure you load EVERY article you read into your reference manager, even if it doesn’t seem very relevant at the time.

2.2 – Build an organised catalogue

In the beginning, you might feel confident that you can remember who said what, where, and what their main arguments were. Trust me, you won’t. If you do a thorough review of the relevant literature (as you must!), you’re going to read many, many articles, and it’s simply impossible to remember who said what, when, and in what context . Also, without the bird’s eye view that a catalogue provides, you’ll miss connections between various articles, and have no view of how the research developed over time. Simply put, it’s essential to build your own catalogue of the literature.

I would suggest using Excel to build your catalogue, as it allows you to run filters, colour code and sort – all very useful when your list grows large (which it will). How you lay your spreadsheet out is up to you, but I’d suggest you have the following columns (at minimum):

• Author, date, title – Start with three columns containing this core information. This will make it easy for you to search for titles with certain words, order research by date, or group by author.
• Categories or keywords – You can either create multiple columns, one for each category/theme and then tick the relevant categories, or you can have one column with keywords.
• Key arguments/points – Use this column to succinctly convey the essence of the article, the key arguments and implications thereof for your research.
• Context – Note the socioeconomic context in which the research was undertaken. For example, US-based, respondents aged 25-35, lower- income, etc. This will be useful for making an argument about gaps in the research.
• Methodology – Note which methodology was used and why. Also, note any issues you feel arise due to the methodology. Again, you can use this to make an argument about gaps in the research.
• Quotations – Note down any quoteworthy lines you feel might be useful later.
• Notes – Make notes about anything not already covered. For example, linkages to or disagreements with other theories, questions raised but unanswered, shortcomings or limitations, and so forth.

If you’d like, you can try out our free catalog template here (see screenshot below).

2.3 – Digest and synthesise

Most importantly, as you work through the literature and build your catalogue, you need to synthesise all the information in your own mind – how does it all fit together? Look for links between the various articles and try to develop a bigger picture view of the state of the research. Some important questions to ask yourself are:

• What answers does the existing research provide to my own research questions ?
• Which points do the researchers agree (and disagree) on?
• How has the research developed over time?
• Where do the gaps in the current research lie?

To help you develop a big-picture view and synthesise all the information, you might find mind mapping software such as Freemind useful. Alternatively, if you’re a fan of physical note-taking, investing in a large whiteboard might work for you.

Step 3: Outline and write it up!

Once you’re satisfied that you have digested and distilled all the relevant literature in your mind, it’s time to put pen to paper (or rather, fingers to keyboard). There are two steps here – outlining and writing:

3.1 – Draw up your outline

Having spent so much time reading, it might be tempting to just start writing up without a clear structure in mind. However, it’s critically important to decide on your structure and develop a detailed outline before you write anything. Your literature review chapter needs to present a clear, logical and an easy to follow narrative – and that requires some planning. Don’t try to wing it!

Naturally, you won’t always follow the plan to the letter, but without a detailed outline, you’re more than likely going to end up with a disjointed pile of waffle , and then you’re going to spend a far greater amount of time re-writing, hacking and patching. The adage, “measure twice, cut once” is very suitable here.

In terms of structure, the first decision you’ll have to make is whether you’ll lay out your review thematically (into themes) or chronologically (by date/period). The right choice depends on your topic, research objectives and research questions, which we discuss in this article .

Once that’s decided, you need to draw up an outline of your entire chapter in bullet point format. Try to get as detailed as possible, so that you know exactly what you’ll cover where, how each section will connect to the next, and how your entire argument will develop throughout the chapter. Also, at this stage, it’s a good idea to allocate rough word count limits for each section, so that you can identify word count problems before you’ve spent weeks or months writing!

PS – check out our free literature review chapter template…

3.2 – Get writing

With a detailed outline at your side, it’s time to start writing up (finally!). At this stage, it’s common to feel a bit of writer’s block and find yourself procrastinating under the pressure of finally having to put something on paper. To help with this, remember that the objective of the first draft is not perfection – it’s simply to get your thoughts out of your head and onto paper, after which you can refine them. The structure might change a little, the word count allocations might shift and shuffle, and you might add or remove a section – that’s all okay. Don’t worry about all this on your first draft – just get your thoughts down on paper.

Once you’ve got a full first draft (however rough it may be), step away from it for a day or two (longer if you can) and then come back at it with fresh eyes. Pay particular attention to the flow and narrative – does it fall fit together and flow from one section to another smoothly? Now’s the time to try to improve the linkage from each section to the next, tighten up the writing to be more concise, trim down word count and sand it down into a more digestible read.

Once you’ve done that, give your writing to a friend or colleague who is not a subject matter expert and ask them if they understand the overall discussion. The best way to assess this is to ask them to explain the chapter back to you. This technique will give you a strong indication of which points were clearly communicated and which weren’t. If you’re working with Grad Coach, this is a good time to have your Research Specialist review your chapter.

Finally, tighten it up and send it off to your supervisor for comment. Some might argue that you should be sending your work to your supervisor sooner than this (indeed your university might formally require this), but in my experience, supervisors are extremely short on time (and often patience), so, the more refined your chapter is, the less time they’ll waste on addressing basic issues (which you know about already) and the more time they’ll spend on valuable feedback that will increase your mark-earning potential.

Literature Review Example

In the video below, we unpack an actual literature review so that you can see how all the core components come together in reality.

Let’s Recap

In this post, we’ve covered how to research and write up a high-quality literature review chapter. Let’s do a quick recap of the key takeaways:

• It is essential to understand the WHY of the literature review before you read or write anything. Make sure you understand the 4 core functions of the process.
• The first step is to hunt down the relevant literature . You can do this using Google Scholar, your university database, the snowballing technique and by reviewing other dissertations and theses.
• Next, you need to log all the articles in your reference manager , build your own catalogue of literature and synthesise all the research.
• Following that, you need to develop a detailed outline of your entire chapter – the more detail the better. Don’t start writing without a clear outline (on paper, not in your head!)
• Write up your first draft in rough form – don’t aim for perfection. Remember, done beats perfect.
• Refine your second draft and get a layman’s perspective on it . Then tighten it up and submit it to your supervisor.

Psst… there’s more!

This post is an extract from our bestselling short course, Literature Review Bootcamp . If you want to work smart, you don't want to miss this .

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38 Comments

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You’re welcome, Yinka. Thank you for the kind words. All the best writing your literature review.

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Thank you. I requested to download the free literature review template, however, your website wouldn’t allow me to complete the request or complete a download. May I request that you email me the free template? Thank you.

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What is a literature review?

A literature review is an integrated analysis -- not just a summary-- of scholarly writings and other relevant evidence related directly to your research question.  That is, it represents a synthesis of the evidence that provides background information on your topic and shows a association between the evidence and your research question.

A literature review may be a stand alone work or the introduction to a larger research paper, depending on the assignment.  Rely heavily on the guidelines your instructor has given you.

Why is it important?

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Discovers relationships between research studies/ideas.
• Identifies major themes, concepts, and researchers on a topic.
• Identifies critical gaps and points of disagreement.
• Discusses further research questions that logically come out of the previous studies.

APA7 Style resources

APA Style Blog - for those harder to find answers

1. Choose a topic. Define your research question.

Your literature review should be guided by your central research question.  The literature represents background and research developments related to a specific research question, interpreted and analyzed by you in a synthesized way.

• Make sure your research question is not too broad or too narrow.  Is it manageable?
• Begin writing down terms that are related to your question. These will be useful for searches later.
• If you have the opportunity, discuss your topic with your professor and your class mates.

2. Decide on the scope of your review

How many studies do you need to look at? How comprehensive should it be? How many years should it cover? 

• This may depend on your assignment.  How many sources does the assignment require?

3. Select the databases you will use to conduct your searches.

Make a list of the databases you will search. 

Where to find databases:

• use the tabs on this guide
• Find other databases in the Nursing Information Resources web page
• More on the Medical Library web page
• ... and more on the Yale University Library web page

4. Conduct your searches to find the evidence. Keep track of your searches.

• Use the key words in your question, as well as synonyms for those words, as terms in your search. Use the database tutorials for help.
• Save the searches in the databases. This saves time when you want to redo, or modify, the searches. It is also helpful to use as a guide is the searches are not finding any useful results.
• Review the abstracts of research studies carefully. This will save you time.
• Use the bibliographies and references of research studies you find to locate others.
• Check with your professor, or a subject expert in the field, if you are missing any key works in the field.
• Ask your librarian for help at any time.
• Use a citation manager, such as EndNote as the repository for your citations. See the EndNote tutorials for help.

Review the literature

Some questions to help you analyze the research:

• What was the research question of the study you are reviewing? What were the authors trying to discover?
• Was the research funded by a source that could influence the findings?
• What were the research methodologies? Analyze its literature review, the samples and variables used, the results, and the conclusions.
• Does the research seem to be complete? Could it have been conducted more soundly? What further questions does it raise?
• If there are conflicting studies, why do you think that is?
• How are the authors viewed in the field? Has this study been cited? If so, how has it been analyzed?

Tips: 

• Review the abstracts carefully.  
• Keep careful notes so that you may track your thought processes during the research process.
• Create a matrix of the studies for easy analysis, and synthesis, across all of the studies.
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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

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Literature Review for Grad Students in Education

• Library Guide: Literature Review

Introduction to Literature Review

If you cannot access the above video, you can watch it here

What is a Literature Review

  The purpose of an academic research paper is to express and document an original idea. Literature Review is one part of that process of writing a research paper. In a research paper, you use the literature as a starting point, a building block and as evidence of a new insight. The goal of the literature review is only to summarize and synthesize the arguments and ideas of others. You should not present your original idea.

The reading that you do as part of a literature review will answer one of two questions:

“What do we know about the subject of our study?” “Based on what we know, what conclusions can we draw about the research question?”

Notice that the conclusions to be drawn are about the research question , as opposed to a novel theory. 

The types of conclusions about your research question that you want to discover are: ❖ gaps in the knowledge on a subject area ❖ questions about your topic that remain unanswered ❖ areas of disagreement in your subject area that need to be settled.

Purpose of Literature Review?

There are a number of differing descriptions of the purpose of a literature review. Primarily it is a tool for

❖ researching the history of scholarly publication on a topic

❖ becoming aware of the scholarly debate within a topic

❖  a summary or restatement of conclusions from research which has been published

❖ synthesis or recombining, comparing and contrasting, the ideas of others.

❖ evaluate sources

❖ search for gaps

A literature review provides a comprehensive overview of a topic , supporting the fundamental purpose of a research paper, which is to present a new point of view or insight on a topic. The literature review supports the new insight. It does not present or argue for it.

Structure of Literature Review

• Choose a topic
• Find research
• Organize sources/notetaking
• Evaluate Sources
• Synthesize: think of this phase as a narrative . 

There are various ways of organizing the literature review process- if one of these seems closer to your purpose, try it out.

Different Types of Literature Sources

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Conduct a literature review

What is a literature review.

A literature review is a summary of the published work in a field of study. This can be a section of a larger paper or article, or can be the focus of an entire paper. Literature reviews show that you have examined the breadth of knowledge and can justify your thesis or research questions. They are also valuable tools for other researchers who need to find a summary of that field of knowledge.

Unlike an annotated bibliography, which is a list of sources with short descriptions, a literature review synthesizes sources into a summary that has a thesis or statement of purpose—stated or implied—at its core.

How do I write a literature review?

Step 1: define your research scope.

• What is the specific research question that your literature review helps to define?
• Are there a maximum or minimum number of sources that your review should include?

Ask us if you have questions about refining your topic, search methods, writing tips, or citation management.

Step 2: Identify the literature

Start by searching broadly. Literature for your review will typically be acquired through scholarly books, journal articles, and/or dissertations. Develop an understanding of what is out there, what terms are accurate and helpful, etc., and keep track of all of it with citation management tools . If you need help figuring out key terms and where to search, ask us .

Use citation searching to track how scholars interact with, and build upon, previous research:

• Mine the references cited section of each relevant source for additional key sources
• Use Google Scholar or Scopus to find other sources that have cited a particular work

Step 3: Critically analyze the literature

Key to your literature review is a critical analysis of the literature collected around your topic. The analysis will explore relationships, major themes, and any critical gaps in the research expressed in the work. Read and summarize each source with an eye toward analyzing authority, currency, coverage, methodology, and relationship to other works. The University of Toronto's Writing Center provides a comprehensive list of questions you can use to analyze your sources.

Step 4: Categorize your resources

Divide the available resources that pertain to your research into categories reflecting their roles in addressing your research question. Possible ways to categorize resources include organization by:

• methodology
• theoretical/philosophical approach

Regardless of the division, each category should be accompanied by thorough discussions and explanations of strengths and weaknesses, value to the overall survey, and comparisons with similar sources. You may have enough resources when:

• You've used multiple databases and other resources (web portals, repositories, etc.) to get a variety of perspectives on the research topic.
• The same citations are showing up in a variety of databases.

Additional resources

Undergraduate student resources.

• Literature Review Handout (University of North Carolina at Chapel Hill)
• Learn how to write a review of literature (University of Wisconsin-Madison)

Graduate student and faculty resources

• Information Research Strategies (University of Arizona)
• Literature Reviews: An Overview for Graduate Students (NC State University)
• Oliver, P. (2012). Succeeding with Your Literature Review: A Handbook for Students [ebook]
• Machi, L. A. & McEvoy, B. T. (2016). The Literature Review: Six Steps to Success

Graustein, J. S. (2012). How to Write an Exceptional Thesis or Dissertation: A Step-by-Step Guide from Proposal to Successful Defense [ebook]

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• Published: 27 April 2024

Advancing the local climate zones framework: a critical review of methodological progress, persisting challenges, and future research prospects

• Jie Han   ORCID: orcid.org/0009-0003-3165-631X 1 ,
• Jingyi Cai 1 ,
• Leixin Ouyang 2 &
• Zhengxuan Liu   ORCID: orcid.org/0000-0002-2761-5078 3  

Humanities and Social Sciences Communications volume  11 , Article number:  538 ( 2024 ) Cite this article

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The local climate zones (LCZs) classification system has emerged as a more refined method for assessing the urban heat island (UHI) effect. However, few researchers have conducted systematic critical reviews and summaries of the research on LCZs, particularly regarding significant advancements of this field in recent years. This paper aims to bridge this gap in scientific research by systematically reviewing the evolution, current status, and future trends of LCZs framework research. Additionally, it critically assesses the impact of the LCZs classification system on climate-responsive urban planning and design. The findings of this study highlight several key points. First, the challenge of large-scale, efficient, and accurate LCZs mapping persists as a significant issue in LCZs research. Despite this challenge, the universality, simplicity, and objectivity of the LCZs framework make it a promising tool for a wide range of applications in the future, especially in the realm of climate-responsive urban planning and design. In conclusion, this study makes a substantial contribution to the advancement of LCZs research and advocates for the broader adoption of this framework to foster sustainable urban development. Furthermore, it offers valuable insights for researchers and practitioners engaged in this field.

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Introduction.

Urbanization is an irreversible process that will continue to accelerate over the next three decades, resulting in a projected global urban population increase of up to 668 million (UN-Habitat 2022 ). While urbanization brings economic development, cultural exchange, and technological progress, it also concentrates people in cities, leading to higher greenhouse gas emissions and pollutants. These emissions contribute to air quality degradation, global warming, and climate change. Urban heat island (UHI), characterized by higher temperatures in urban areas compared to their surrounding rural areas, is a consequence of urbanization, driven by unique urban surfaces and anthropogenic heat release. UHI carries numerous adverse effects, including increased energy consumption, air pollution, degradation of living conditions, and elevated heat-related mortality rates. All of these challenges significantly impede sustainable development, underscoring the critical importance of identifying, mitigating, and adapting to UHI (Huang and Lu 2018 ).

The term “urban heat island” was first introduced by Balchin and Pye ( 1947 ), and it has since become a prominent research field within urban climate studies (Peng et al. 2022 , Zhang et al. 2022 , Mo et al. 2024 ). The central issue in UHI research revolves around quantifying urban heat island intensity (UHII) (Huang and Lu 2018 ). The conventional approach to UHI evaluation involves computing UHII by comparing the average temperature difference between urban and rural areas. However, this method encounters limitations due to the diverse nature of urban morphology, land cover, and human activities, leading to varying UHII results within urban areas. Consequently, UHI analysis and mitigation strategies based on these results lack precision. Another challenge with the urban-rural dichotomy lies in selecting suburban measurement points that are minimally affected by urbanization. With urbanization, the once-clear social, political, and economic boundaries between urban and rural areas have blurred. It is more accurate to describe the relationship between urban and rural areas as a continuous and dynamic system rather than a rigid dichotomy.

To address the shortcomings of the traditional “urban-rural dichotomy” in UHI research, the local climate zones (LCZs) classification system, introduced by Stewart and Oke ( 2012 ), offers a fresh research framework. This system has expanded its applications beyond UHI research and is now being employed in other domains related to sustainable urban development, including urban planning (Pradhesta et al. 2019 , Kopp et al. 2021 ), building energy consumption (Yang et al. 2020a , 2022 , Benjamin et al. 2021 ), and urban thermal comfort (Lau et al. 2019 , Wu et al. 2022 ).

Table 1 lists the existing review articles on LCZs research. Many researchers in the domain of LCZs mapping have directed their attention to the current advancements in this area. For instance, Huang et al. ( 2023 ) offered a comprehensive review of LCZs mapping, providing detailed analyses of remote sensing (RS)-based and geographic information system (GIS)-based methods. They discussed RS-based methods in terms of feature sets, classification units, training areas, classification algorithms, and accuracy assessment, while GIS-based methods were elaborated based on LCZ parameters, basic spatial units (BSUs), classification algorithms, and accuracy assessment. Quan and Bansal ( 2021 ) summarized the general LCZs mapping processes in the reviewed studies, encompassing data collection, defining BSUs, calculating urban canopy parameters (UCPs), LCZs classification, post-processing, and performance evaluation. Ma et al. ( 2021 ) conducted a timely investigation into RS-based LCZs mapping applications. They analyzed and evaluated several aspects influencing LCZs mapping performance, including mapping units/scales, transferability, sample datasets, low accuracy, and classification schemes. Meanwhile, researchers have dedicated their focus to the field pertaining to the LCZs framework. For example, Lehnert et al. ( 2021 ) provided a comprehensive analysis of the application of the LCZs framework in European urban areas, demonstrating an increasing and widely recognized use of LCZs in climate research across European cities. Xue et al. ( 2020 ) explored the applications of LCZs schemes in various research fields such as meteorology, atmospheric science, environmental science, remote sensing, architectural technology, civil engineering, and ecology by conducting a bibliometric analysis of articles citing LCZs using CiteSpace. Additionally, most review studies utilize bibliometric analysis to review LCZs research. However, bibliometric analysis has the limitation of time lag due to the literature on which it is based, which can not sufficiently reflect the latest research progress.

The mentioned studies indicate the significant attention LCZs-related research has garnered within the academic community. Nonetheless, several noticeable gaps exist: 1) Few researchers have systematically conducted critical reviews and comprehensive summaries of LCZs research, especially concerning its recent notable advancements. 2) A thorough investigation into its development, research methodologies, and broader applications, particularly in sustainable urban development contexts, is warranted. This paper’s innovations and contributions primarily involve:

1) Given recent advancements, this study comprehensively examines and categorizes research methods and application areas within the LCZs framework. This analysis provides a thorough understanding of theoretical foundations and practical applications, contributing to a more holistic comprehension of LCZs studies.

2) The paper critically evaluates the effectiveness of the LCZs classification system in supporting climate-responsive urban planning and design. This assessment is crucial in understanding the practical utility of the LCZs framework for sustainable urban development and its potential to mitigate UHI challenges.

The primary sections of this paper are structured as follows: The literature survey and corresponding quantitative analysis are presented in Literature Survey. Advancements in local climate zones framework introduces the LCZs framework and delves into the measurement of UCPs. Recent advancements in manual sampling and mapping methods of LCZs reviews the progress of LCZs research methods applied in UHI research. Application of LCZs framework in various scenarios explores the various application areas of LCZs, with a particular focus on its utility in UHI research and climate-sensitive urban design. Limitations, challenges, and future prospects engages in a discussion regarding research limitations and potential future applications of the LCZs framework. Conclusions presents the key findings and conclusions drawn from the study. This structured approach allows for a systematic and in-depth exploration of the LCZs classification system’s development and its multifaceted applications in the context of research related to sustainable urban development.

Literature survey

This study conducted a comprehensive screening of all peer-reviewed journal and conference papers that cited the original LCZs framework articles based on the Web of Science dataset. As of February 2023, a total of 1534 papers were identified. Based on this, we performed literature statistics and bibliometric analysis to quantitatively assess the current state of development of LCZs research.

Literature statistics

The literature statistics were conducted from three aspects: annual output, country distribution, and research fields. Figures 1 and 2 provide visual representations of the annual output and the country distribution of LCZs research for the period spanning from 2013 to 2022. Since the introduction of the LCZs framework in 2012, there has been a notable surge in publications related to LCZs research. Specifically, the number of publications has seen a substantial increase, starting at 17 in 2013 and reaching 300 in 2022. This upward trend underscores the escalating interest and engagement in LCZs research within the academic community and beyond. Furthermore, the distribution of countries reveals five nations that have made substantial contributions to LCZs research. China stands out with the highest number of papers, accounting for 668 publications, which amounts to approximately 43.55% of the total papers. Following China, the United States, Germany, the United Kingdom, and Australia have also made significant contributions to LCZs research, with 333, 225, 176, and 104 publications, respectively. These statistics highlight the global reach and significance of LCZs research, with diverse countries actively participating in advancing this research field.

Annual output of LCZs research.

Country distribution of LCZs research.

Table 2 provides an overview of the distribution of research fields related to LCZs. LCZs research is characterized by its interdisciplinary nature, encompassing a wide spectrum of academic disciplines. The research content of LCZs studies spans several fields: (1) Meteorology and atmospheric sciences: The LCZs framework is employed to investigate urban meteorology, evaluate the impact of urbanization on weather patterns, and develop models for urban climate simulations; (2) Environmental sciences and ecology: The LCZs classification system helps identify and quantify the effect of urbanization on ecosystems, biodiversity, and the overall environment; (3) Physical sciences: The LCZs classification takes into account physical parameters such as surface materials, building density, and thermal admittance. This classification helps physical scientists study the thermal characteristics of urban surfaces, develop models for energy balance calculations, and explore the impact of different materials on the UHI effect; (4) Geography: Geographers use LCZs framework to investigate urban morphology, land use dynamics, urban-rural interactions, and the relationship between urban form and climate; (5) Energy and fuels: The LCZs classification system helps identify areas with high energy demand or heat stress, guiding the development of energy-efficient buildings, urban cooling techniques, and renewable energy integration; (6) RS: RS is a prominent and integral research direction within LCZs. It involves the use of satellite and aerial imagery to map and monitor large-scale urban climates, often supported by GIS technologies. The multidisciplinary nature of LCZs research enables cross-disciplinary collaboration and knowledge integration, making it a versatile framework for understanding and addressing urban climate challenges.

Bibliometric analysis

The study employs the concept of “co-occurrence clustering” and utilizes the CiteSpace visualization software to conduct a bibliometric analysis of the screening results. In this analysis, the fundamental unit of information extraction and structural construction is the “keywords”. The research utilizes a “keyword co-occurrence” network to depict the knowledge structure, research evolution, and current research focal points within the LCZs application field. In this network, each node corresponds to a keyword found in the literature, and the links represent the connections between these keywords. The objective is to visually and analytically explore the nodes, links, and overall network structure, shedding light on the present state of development in the LCZs application field. This approach allows for a systematic and data-driven examination of the relationships between keywords and their significance within the context of LCZs research. It facilitates the identification of trends, patterns, and emerging areas of interest within this field, providing valuable insights for researchers and practitioners alike.

In the analyzed literature employing the LCZs framework, several recurring nodes stand out, shedding light on the primary objectives and emphases of LCZs research. The top five frequently occurring nodes include “urban heat island,” “temperature,” “climate,” “impact,” and “city,” as illustrated in Fig. 3 . These nodes collectively indicate that LCZs research primarily seeks to understand the factors influencing urban climates (“climate” and “city”), particularly the impact on temperature parameters (“temperature”). There is a notable focus on examining how the factors affect UHI (“urban heat island”), which aligns with the LCZs framework’s original purpose. The high frequency of “urban heat island” (697 times, with 144 mentions in 2021) underscores its central role in LCZs research. This centrality stems from the LCZs framework’s inception, which aimed to address the limitations of the “urban-rural dichotomy” in UHI studies, enabling a more nuanced understanding of UHI impacts and the development of effective mitigation strategies.

Keyword co-present of the analyzed LCZs literature.

Advancements in local climate zones framework

Local climate zone classification system.

LCZs are defined as areas with uniform surface cover, structure, material, and human activity, with a minimum radius of 200–500 m, which exhibit local-scale, climatic nature, and zonal representation as depicted in Fig. 4 . The LCZs classification system is based on 10 UCPs with recommended ranges, allowing for classification into 17 standard LCZ patterns, comprising 10 built types and 7 land cover types. The various LCZ types represent the diverse compositions of buildings, roads, plants, soils, rocks, and water. The names of standard built types primarily reflect three building structure characteristics (Density: compact/open; Height: high/mid/low; Material: heavy/lightweight) and building type (general/industrial). Conversely, the counterparts of standard land cover types mainly reflected the vegetation and land cover characteristics.

Schematic diagram of standard LCZs.

The process of LCZs classification usually involves four steps: data acquisition, UCPs calculation, LCZs classification, and accuracy evaluation. The first step is to collect the required information for the study area (e.g., field measurements and satellite images). The second step involves calculating UCPs using the data gathered in the previous step. A detailed description of the calculation methods for UCPs is provided in Measurement of urban canopy parameters. For LCZs classification, the results from UCPs calculation can assist in identifying the best match between field sites and LCZ classes. Additionally, LCZs subclasses can be customized when UCPs deviate from the recommended ranges of the standard set of classes. For instance, a combination of LCZ 4 (Open high-rise) and 3 (Compact low-rise) can provide LCZ 3 4 (Compact low-rise with open high-rise).

Measurement of urban canopy parameters

For achieving precise LCZs classification, obtaining accurate values for UCPs is of paramount importance. These UCPs are primarily related to surface structure parameters, including sky view factor (SVF) (Steyn 1980 , Matzarakis et al. 2007 , Liang et al. 2017 ), aspect ratio (AR) (Masson 2000 ), and height of roughness elements (HRE) (Yan and Huang 2022 , Wu et al. 2023 ). They also encompass surface cover parameters such as building surface fraction (BSF) (Yu et al. 2010 , Guo et al. 2022 , Jifroudi et al. 2022 , Wei et al. 2023 ), impervious surface fractions (ISF), and pervious surface fractions (PSF) (Deng and Wu 2013 , Sytsma et al. 2020 ). Surface fabric parameters (surface admittance and surface albedo (Bartmiński and Siłuch 2022 , Tahooni et al. 2023 )) and human activity parameters (anthropogenic heat flux (Yu et al. 2021 , Wang et al. 2022b , Liu and Li 2023 )) are equally included.

In the absence of specific heat-related indicators, most current studies rely on the geometric and ground cover values to define LCZs. Table 3 highlights the various methods employed in previous studies to measure parameters related to ground cover and geometry. Measurement methods for SVF are typically categorized as fisheye photographs, satellite images, street view images, and numerical simulations. Parameters such as AR, BSF, ISF, PSF, HRE, and TRC are primarily grouped into three categories: field measurement, satellite image calculation, and building data acquisition.

In summary, methods for measuring UCPs mainly consist of manual measurement and satellite image calculation. Manual measurement involves collecting data from a few sampling points in a region and then averaging them to determine UCP values. However, this approach is time-consuming, labor-intensive, and prone to inaccuracies, rendering it unsuitable for large-scale urban climate studies based on the LCZs framework. In contrast, alternative methods such as RS and simulation modeling can be more effectively employed for UCPs measurements. These methods offer a more efficient and accurate means of collecting UCPs, enabling a comprehensive and reliable analysis of urban climate patterns and their impact on human well-being and the environment. Furthermore, there is a pressing need to establish standardized procedures for measuring UCPs. Future research within the LCZs framework could emphasize the standardization of UCP calculation using RS and GIS data to ensure precise results.

Calculating urban heat island intensity using the LCZs framework

The LCZs framework method focuses on defining the UHI magnitude using the temperature difference between LCZs, represented by ΔT LCZ X-LCZ D , rather than the traditional “urban-rural” temperature difference (ΔT u-r ) (Stewart and Oke 2012 ). Here, LCZ X denotes any class within the LCZs classification system, while the temperature of LCZ D (low plants) serves as the baseline. This calculation method not only offers a more physically grounded understanding of UHII but also enhances its analysis and comparability. Numerous studies have affirmed the efficacy of the LCZs-based UHII calculation method. For example, Shi et al. ( 2021 ) computed surface urban heat island (SUHI) intensity by analyzing the difference in land surface temperature (LST) between LCZs and compared it with the conventional “urban-rural dichotomy” method. The results revealed that the LCZs-based UHII calculation method yielded a more precise measure of SUHI intensity. Similarly, Budhiraja et al. ( 2019 ) examined the seasonal SUHI intensity of Delhi using both LCZs-based and “urban-rural dichotomy” methods, concluding that the former provided a more detailed understanding of the relationship between urban structure and SUHI.

Two primary UHI types were assessed using the LCZs-based UHII calculation method: atmospheric urban heat island (AUHI) and SUHI. Concerning AUHI, Chen et al. ( 2021 ) explored the connection between the diurnal temperature range and AUHI intensity using the LCZs-based UHII calculation method under varying meteorological conditions categorized by precipitation. Yang et al. ( 2017 ) investigated the characteristics of local AUHI at selected LCZ sites, employing the LCZs-based UHII calculation method. Regarding SUHI, Wang et al. ( 2021 ) calculated surface urban heat island intensity (SUHII) using this method and proposed a sustainable urban green infrastructure planning strategy based on the analysis results. O’Malley and Kikumoto ( 2022 ) delved into heat storage in Tokyo Prefecture, utilizing the LCZs-based UHII calculation method to compute nocturnal-diurnal SUHI differences. Finally, Zheng et al. ( 2022 ) scrutinized the changes of LCZs and surface SUHII within Chang-Zhu-Tan’s primary urban area, employing the LCZs-based UHII calculation method.

In conclusion, the LCZs-based UHII calculation method represents a significant advancement in UHI research. Its ability to capture localized UHI variations, enhance comparability across regions, and guide targeted mitigation strategies makes it a valuable tool for urban planning and climate adaptation. However, addressing data challenges and standardization issues will be crucial to fully realize its potential for widespread application. Further research should focus on refining data acquisition and measurement techniques within the LCZs framework to ensure the accuracy and reliability of UHII assessments.

Recent advancements in manual sampling and mapping methods of LCZs research

This section explores the research methods employed within the LCZs framework for UHI research, specifically focusing on the manual sampling method for limited LCZs and LCZs mapping methods for large-scale applications.

Manual sampling method for limited LCZs

In the early stages of UHI research based on the LCZs framework, the primary emphasis was on LCZs classification through a manual sampling approach. This method involved the identification of LCZ types for a limited number of land parcels using manual techniques, such as scrutinizing satellite images, live photos, and conducting field surveys, for urban climate investigations. For instance, Yang et al. ( 2017 ) conducted a study examining the local UHI characteristics across 12 LCZs. These LCZs were selected based on a thorough review of satellite images, street-level views, and on-site fieldwork. In another research endeavor, Yang et al. ( 2018 ) investigated 14 distinct LCZs using field data and high-resolution satellite images to analyze the thermal characteristics of each location.

However, it is important to note that the manual sampling method has limitations, particularly when applied to large-scale urban climate investigations. It necessitates a substantial number of researchers to manually identify the LCZ type of each plot, which is resource-intensive and time-consuming. Moreover, there is a risk of human error during the identification process, potentially compromising the accuracy and reliability of the results. Consequently, while the manual sampling method has proven valuable for in-depth studies focusing on limited LCZs, it may not be suitable for broader urban climate investigations within expansive urban areas. In such cases, alternative LCZs mapping methods are typically preferred to ensure efficiency and accuracy.

LCZs mapping methods

The evolution of the LCZs framework has given rise to LCZs mapping methods tailored for large-scale urban climate studies. These methods simplify the representation of urban climate within the LCZs framework, enabling comparative analyses across different cities and enhancing the universality and applicability of findings. Moreover, LCZs framework facilitates the transformation of “climate language,” supporting the development of climate-sensitive urban design. LCZs mapping methods can be categorized into two types based on their data sources and classification algorithms: GIS-based and RS-based mapping methods (Tamás et al. 2015 ).

GIS-based LCZs mapping method

The GIS-based LCZs mapping method comprises six main steps, as depicted in Fig. 5 (Quan and Bansal 2021 ). Initially, it involves collecting GIS data and defining BSUs to segment the urban environment into smaller blocks for LCZs classification. Subsequently, the UCPs values for each BSU are calculated using GIS data, and the LCZ type for each BSU is determined based on the LCZs framework. Finally, post-processing is carried out to merge adjacent units for simplification and size adjustment, ultimately leading to the generation and evaluation of the LCZs map. BSUs refer to the spatial scale of LCZ classification, and the size of a BSU must meet the size requirement of the LCZs framework. The definition of BSUs is typically divided into lot area polygons (Lelovics et al. 2014 , Unger et al. 2014 ), urban blocks (Wu et al. 2018 , Quan 2019 ), and regular grids (Chen et al. 2020a ). Additionally, pre-processing of the GIS data is often necessary before calculating the UCPs. Common pre-processing includes: (1) Data cleaning: GIS datasets may contain errors or inconsistencies, such as missing values, outliers, or topological errors. It’s important to clean the data to avoid inaccuracies. (2) Spatial resolution matching: GIS datasets may have different spatial resolutions, which can affect the accuracy of UCPs calculations. Pre-processing is necessary to resample or aggregate datasets to a common spatial resolution to ensure compatibility for analysis. (3) Others: Steps such as data normalization and data integration are performed as needed. Overall, pre-processing of GIS data is essential before calculating UCPs to ensure data cleanliness, compatibility, and suitability for analysis, leading to more accurate and reliable results.

General steps of GIS-based LCZs mapping method (Quan and Bansal 2021 ).

The use of GIS-based LCZs mapping has gained traction in urban climate studies since the pioneering study by Lelovics et al. ( 2014 ) in Hungary. For example, Quan et al. ( 2017 ) developed and tested a bottom-up, fine-grained 3D LCZs mapping method utilizing GIS and land cover data, with urban block units serving as BSUs. Geletič et al. ( 2019 ) employed the GIS-based LCZs mapping method to explore the inter-zone and intra-zone seasonal variations of SUHI in three central European cities.

Despite its precision, the GIS-based LCZs mapping method has limitations. Firstly, obtaining accurate and consistent ground truth data for calculating UCPs poses a significant challenge, leading to limited availability of urban data. The inability to acquire comprehensive and detailed datasets for estimating UCPs, particularly those related to thermal aspects, can significantly impact the accuracy of LCZs mapping. Secondly, the merging of BSUs exists in post-processing, making it challenging to find optimal solutions, particularly in intricate urban environments. This process may not fully capture the complexity of LCZs mapping.

RS-based LCZs mapping method

RS is a technology that leverages remote sensors to collect data from target objects and analyze it to extract valuable information. Advances in RS information acquisition, transmission, and storage technologies have diminished the limitations of RS applications due to improved data quality and the increased availability of multiple RS data sources (Liu et al. 2006 ). RS satellites streamline fieldwork complexity and time intervals while delivering quantifiable and qualitative data (Dhingra and Kumar 2019 ). Optical RS imagery is gradually favored for identifying and categorizing land types and has become a pivotal research area.

RS-based LCZs mapping methods also have several limitations. One key limitation is the spatial and temporal resolution of the RS data. RS data may not always provide complete coverage or may be affected by cloud cover, which means that RS images need to be processed for stitching. However, since the spatial and temporal resolution of different remotely sensed images may vary, the stitching process may impact the accuracy and completeness of the LCZs mapping. Additionally, RS-based LCZs mapping requires specialized knowledge in remote sensing and image processing, which can be a barrier for non-remote sensing professionals. This limitation restricts the widespread application of RS-based LCZs mapping in urban planning and climate studies.

However, compared to GIS-based approaches, RS-based LCZs mapping methods offer several advantages, including higher resolution, finer spatial and temporal data, and the ability to quickly cover large areas. As a result, RS-based LCZs mapping has become the preferred approach for LCZs classification.

To enhance the accuracy of LCZs map classification, RS researchers have employed various benchmark datasets and classifiers. Regarding the benchmark dataset, Hu et al. ( 2018 ) utilized Sentinel-1 Dual-Pol data in LCZs mapping. Yang et al. ( 2020b ) employed multi-source datasets, including Luojia1-01 nighttime light imagery, Landsat-8, Sentinel-2, and building vector data, to generate LCZs maps. They found that a combination of object-based and pixel-based data with multi-source data improved LCZs mapping workflow. Machine learning classifiers, such as random forests and support vector machines (Xu et al. 2017 , Hu et al. 2018 , Hay Chung et al. 2021 ), are widely used for LCZs classification based on free multi-temporal RS data. In recent years, deep learning techniques have also been employed in RS-based LCZs mapping, as artificial intelligence has advanced. For example, Liu et al. ( 2019 ) combined object-based image analysis with convolutional neural networks (CNN) for LCZs mapping. Huang et al. ( 2021 ) introduced a CNN-based LCZ classification model for LCZs mapping in 32 Chinese cities. Their model achieved high overall accuracy in more than 50% of the cities.

Urban climate studies based on the LCZs framework face notable challenges due to the demand for expertise in meteorological science, RS, and machine learning, as well as data availability issues and non-standardized urban description methods. To address these challenges, Bechtel et al. ( 2015 ) proposed the world urban database and access portal tool (WUDAPT) protocol for LCZs mapping, which was developed ultimately into the LCZs generator (Demuzere et al. 2021 ), an online platform that generates LCZs mapping solely needing a training area file as input and also provides automated accuracy assessment. This approach aims to collect, store, and disseminate climate-related data on urban physical geography globally. The WUDAPT approach merges local expert knowledge with the LCZs framework to categorize the urban landscape into LCZs, generating LCZs maps for urban regions. The WUDAPT, outlined in Fig. 6 , has been widely adopted for urban climate studies in numerous regions. For example, Demuzere et al. ( 2022 ) generated a 100 m-resolution global LCZs map, accessible for download at https://doi.org/10.5281/zenodo.6364594 . Cai et al. ( 2018 ) created an LCZs map for the Yangtze River Delta megaregion in China. Ren et al. ( 2019 ) generated LCZs maps for over 20 cities and three major economic regions in China, offering recommendations for enhancement. Demuzere et al. ( 2019 ) constructed LCZs maps for Europe. Beyond urban climate studies, WUDAPT finds applications in various domains, including urban pollution (Shi et al. 2019 ) and multi-scale urban atmospheric modeling (Ching et al. 2019 ).

WUDAPT workflow (Bechtel et al. 2015 ).

LCZs mapping methods represent a pivotal advancement within the LCZs framework, enabling more extensive and systematic urban climate studies. These methods are indispensable for gaining insights into urban climatology, which is crucial for informed urban planning and climate-responsive urban design. While both GIS-based and RS-based LCZs mapping methods offer advantages, it’s essential to consider their respective strengths and limitations. GIS-based approaches provide high precision but may suffer from data availability issues and the complexity of post-processing. In contrast, RS-based methods offer freely available multi-temporal data and can quickly capture large-scale urban environments but may require extensive computational resources and expertise. The integration of machine learning and deep learning techniques into RS-based LCZs mapping has significantly improved classification accuracy and efficiency. However, these methods often demand large training datasets and computational resources. Further research should focus on optimizing these techniques for resource-constrained environments. The WUDAPT protocol stands out as a promising approach for LCZs mapping, offering generality, simplicity, and objectivity. Its reliance on local expert knowledge enhances accuracy, especially in areas with limited data availability. However, challenges persist in implementing this protocol universally, particularly in regions lacking local expertise.

In summary, LCZs mapping methods represent a pivotal milestone in urban climate research. They offer versatile tools for understanding and addressing the UHI effect and other climate-related urban challenges. As technology and data availability continue to advance, these methods are poised to play an increasingly prominent role in shaping sustainable and climate-resilient cities.

Application of LCZs framework in various scenarios

The application domains of the LCZs framework can be categorized and analyzed based on the keywords found in the screened literature. This analysis spans three principal areas: (1) LCZs framework in UHI studies: The primary application of the LCZs framework remains in the domain of UHI research. It provides a valuable tool for investigating the causes and consequences of UHIs, helping researchers better comprehend their impacts on urban climates and devising strategies to mitigate them. Given the growing significance of UHI effects in urban areas, continued research in this area is essential. (2) LCZs research contributions to urban design and climate change mitigation: LCZs research also makes substantial contributions to urban design and climate change mitigation efforts. The framework enables a more refined understanding of how urban structures and land use impact local climates. Consequently, it aids urban planners and policymakers in developing climate-sensitive urban designs and strategies to reduce the UHI effect and its associated challenges. (3) LCZs framework in diverse fields: LCZs research has found applications in various other domains, such as urban ventilation, precipitation, thermal comfort, carbon emissions, and building energy consumption. This indicates the versatility of the LCZs framework and its potential to inform a broad spectrum of urban-related research.

In summary, the LCZs framework has evolved to become a valuable tool in various research scenarios. While its origins lie in addressing UHI research limitations, it now extends its influence to inform urban design, climate change mitigation, and a range of interdisciplinary studies. Its adaptability and versatility underscore the continued relevance of LCZs research in addressing contemporary urban challenges.

LCZs framework in urban heat island studies

UHI research is crucial for understanding the impact of urban environments and devising strategies to mitigate UHI effects. Traditional studies have focused on 2D built environment parameters, such as building density, road density, and green space area, extracted from available data sources like weather data or satellite imagery for 2D planar UHI studies. Recent investigations have revealed that 3D built environment factors, including building height and SVF, have a more substantial influence on UHI than the 2D parameters (Luo et al. 2023 ). Consequently, there is a growing need for research that assesses and characterizes UHI through 3D spatial analysis, rather than the planar UHI estimation (Kim and Brown 2021 ). The LCZs system, which integrates both 2D and 3D UCPs, is well-suited for 3D UHI studies and can contribute to advancing the understanding of UHI and its influencing factors.

Table 4 provides examples of UHI research conducted using the LCZs framework, covering various climate types and research contents. These studies span different climate types, including tropical, subtropical, temperate, and more. UHI research typically falls into two categories: SUHI, which concerns the temperature difference between urban and rural areas at the surface level, and AUHI, which examines corresponding air temperature differences. Temperature variables in UHI studies can further be categorized into LST and air temperature, depending on the type of UHI under investigation. Research objectives encompass the identification, influencing factors, and mitigation strategies associated with UHI. UHI studies employ four primary measurement methods, including fixed measurement (utilizing fixed meteorological stations or establishing stationary observation points for thermal environment measurements), mobile measurement (employing mobile vehicles equipped with climate observation instruments to collect and record climate data along predefined routes), ground measurement (retrieving LST using thermal infrared data), and numerical simulation.

Given the dispersed nature of measurement points and the limited equipment available for LCZs investigations, many UHI studies opt for mobile measurement or LST retrieval methods to gather temperature data across extensive areas. Furthermore, contemporary LCZs framework research has shifted its focus from single-city examinations to comparative analyses between cities. This shift highlights the generalizability of the LCZs framework and its contributions to the growing trend of multi-regional urban climate research.

LCZs research contributions to urban design and climate change mitigation

Well-planned cities are essential for achieving sustainable urban development (Bai 2018 ). Climate-sensitive urban design plays a pivotal role in addressing the challenges posed by rising temperatures, which threaten residents’ thermal comfort (Kim and Brown 2021 ). However, existing urban planning systems struggle to cope with the complexities of local, regional, and global warming. Integrating climate considerations into data requirements and analysis methods is crucial for practical urban design applications (Perera and Emmanuel 2018 ).

The development of urban climate mapping systems has emerged as a responsive tool for climate-conscious urban planning. LCZs offer a structured classification system for land surface characteristics, forming the basis for surface parameterization methods (Ren et al. 2011 , Jin et al. 2020 ). LCZs facilitate the examination of the relationship between urban morphology and climate, providing meteorological data that informs building and urban design decisions. This framework has yielded significant insights into climate-responsive urban design, as exemplified by recent research endeavors.

For instance, Perera and Emmanuel ( 2018 ) utilized the LCZs framework to guide urban planning in Colombo, establishing it as a valuable theoretical foundation for crafting climate-sensitive cities. Likewise, Maharoof et al. ( 2020 ) applied the LCZs framework to investigate the implementation of climate-sensitive urban planning in densely populated urban areas, as illustrated by their case study of Glasgow city center. Another study by Pradhesta et al. ( 2019 ) dissected the critical components of thermal comfort within the LCZs framework, emphasizing factors such as roughness feature height, packing density, surface cover, and thermal admittance of materials. These components prove pivotal in the design of urban spaces that prioritize residents’ thermal comfort.

In essence, the LCZs framework offers a powerful tool for formulating climate-sensitive urban design strategies that enhance the quality of life and the sustainability of our cities. Climate-conscious urban design based on LCZs revolves around several key facets:

i) Green infrastructure: Integrating green infrastructure into urban planning stands as a critical measure for mitigating the effects of climate change on cities and their inhabitants. A comprehensive evaluation by Emmanuel and Loconsole ( 2015 ) underscores the effectiveness of green infrastructure options in combatting urban overheating, particularly within the context of a warming climate. Notably, increasing green coverage by approximately 20% over current levels could potentially eliminate up to half of the projected extra UHI effect by 2050 (Emmanuel and Loconsole 2015 ). Further insights from Kotharkar et al. ( 2020 ) reveal that greening initiatives not only serve as cooling strategies but also enhance pedestrian-level comfort. Intriguingly, their research highlights the superior results achieved by planting vegetation along streets, as opposed to concentrating greenery in designated areas. Li et al. ( 2022b ) further advocate for the moderation of SUHI through the strategic implementation of urban blue-green infrastructure. Stepani and Emmanuel ( 2022 ) advocate optimizing green spaces within public realms rather than merely increasing their quantity, emphasizing that climate-responsive design necessitates a diverse array of solutions, extending beyond green infrastructure.

ii) Blue infrastructure: The concept of blue infrastructure encompasses a network of natural and artificial water systems, including rivers, lakes, canals, and drainage systems, which serve as vital resources for human communities. Li et al. ( 2022b ) recommended harnessing the seasonal variations and spatial distribution of water bodies to enhance the cooling performance of LCZ G (Water). Factors such as distance and flow rates within rivers significantly influence the cooling effects, making them key considerations for urban planners and policymakers. Furthermore, they stress the importance of accounting for the growing risks of floods and droughts in East African cities, necessitating the design of blue infrastructure capable of adapting to seasonal variations and changing climates.

iii) Building design: Building resilience to climate change-induced extreme weather events is a crucial consideration in urban design. Passive cooling strategies, including cool roofs, emerge as effective means to reduce energy consumption and mitigate the UHI effect. Kotharkar et al. ( 2020 ) highlight the efficacy of cool roofs, specially designed to reflect more sunlight and absorb less heat than traditional roofing materials, particularly in densely populated urban areas.

iv) Street design: Urban streets represent a significant component of contemporary urban planning, encompassing approximately one-quarter of urban areas. They wield considerable influence in shaping comfortable urban environments. However, the climate-sensitive street design goes beyond rigid one-size-fits-all approaches. Maharoof et al. ( 2020 ) advocate for the integration of LCZ parameters with form-based considerations such as orientation and façade geometry. This nuanced approach recognizes that different street typologies may demand distinct design strategies, underscoring the importance of tailoring designs to specific urban contexts.

v) Other considerations: Research by O’Malley and Kikumoto ( 2022 ) suggests that mitigating UHI effects can be achieved through constructing lower-rise and open LCZs. They note that high-rise buildings possess larger heat storage capacities relative to lower-rise structures. Additionally, Zheng et al. ( 2022 ) proposed the full utilization of the cooling potential inherent in LCZ A-D and LCZ G and emphasized the need for judicious regulation of construction land areas (built LCZs) in future urban development plans.

Leveraging insights from LCZs-based research, climate-sensitive urban design should center around the integration of green and blue infrastructure, innovative building design, and flexible street design elements to counter the adverse impacts of climate change and foster the creation of sustainable, climate-responsive urban environments.

i) Green-blue infrastructure: Urban areas can benefit significantly from nature-based solutions, such as green roofs, gardens, and urban forests. These solutions serve dual purposes, including mitigating the negative impacts of climate change and promoting biodiversity. Furthermore, green corridors, such as tree-lined streets and bike paths, serve as multifunctional assets. They not only improve air quality but also offer enhanced mobility options for residents and reduce noise pollution. Water features, such as fountains and ponds, not only enhance the aesthetic appeal of public spaces but also provide cooling through evaporation.

ii) Building design: To mitigate UHI effects, building design should incorporate various strategies, including green roofs, cool roofs, shade provision, and sustainable materials. Green roofs are particularly advantageous because they contribute to cooling both buildings and their surroundings by absorbing and subsequently releasing moisture through transpiration. Additionally, cool roofs reflect sunlight and possess lower heat absorption than traditional roofing materials. The reduction in heat transfer into buildings beneath the roof not only lowers cooling costs but also enhances indoor comfort during hot weather. Moreover, building design can introduce shading solutions in outdoor areas, thereby reducing the amount of sunlight absorbed by buildings and their surroundings, thus contributing to cooler environments. Sustainable building materials, such as recycled steel, bamboo, and reclaimed wood, can play a pivotal role in reducing the environmental footprint of construction, ensuring that buildings are more sustainable, efficient, and comfortable.

iii) Street design: The design of urban streets plays a crucial role in mitigating UHI effects. Incorporating vegetation, green roofs, and other green elements into street design can effectively provide shade and evaporative cooling. Furthermore, using permeable pavement materials allows rainwater to penetrate the surface, promoting evaporation and reducing the amount of heat absorbed and re-emitted by the pavement. This is particularly important as impervious surfaces, like concrete and asphalt, tend to absorb and re-emit substantial amounts of heat, exacerbating UHI effects. By reducing the prevalence of impervious surfaces in street design, the adverse impacts of UHI can be mitigated. Additionally, thoughtful street furniture design, including streetlights and bus shelters, can be employed to provide shade and further reduce UHI effects.

In summary, urban design strategies that incorporate green-blue infrastructure, utilize innovative building design techniques, and employ street design elements prioritizing vegetation and sustainability offer comprehensive solutions to mitigate the adverse effects of UHI. These strategies enhance the overall resilience and comfort of urban areas, preparing them for the challenges posed by climate change.

Applications of the LCZs framework in other domains

Urban climate studies.

Beyond its primary application in UHI studies, the LCZs framework offers substantial utility across various domains of urban climate research. This adaptable framework enables researchers to explore both spatial and temporal dynamics of ventilation and precipitation patterns at a local scale, providing crucial insights for developing effective strategies to mitigate the environmental and health impacts of urbanization. For instance, Zhao et al. ( 2020 ) effectively employed the LCZs framework to analyze local-scale urban ventilation performance in Shenyang. In another study, Yang et al. ( 2019a ) evaluated the ventilation efficiency of different LCZs in Shanghai by assessing the frontal area index across various LCZ types. Chen et al. ( 2021 ) conducted a quantitative assessment of the relationship between daily temperature variations and UHII under varying meteorological conditions, classifying data using precipitation as a criterion. Additionally, Shi et al. ( 2022 ) assessed the influence of urban ventilation corridors on UHII using the LCZs framework. Yang et al. ( 2020c ) explored the spatial and temporal variations in humidity within the urban canopy across eight LCZ plots in Nanjing, analyzing the interplay between humidity differences, condensation precipitation events, meteorological parameters, and UHI. In a related study, Savić et al. ( 2020 ) scrutinized precipitation patterns in different urbanization settings by segregating areas into “urbanized” and “non-urbanized” based on LCZs classifications.

In summation, the utilization of the LCZs framework within urban climate research enhances our comprehension of the intricate connections between urban design and the multifaceted facets of urban climate. This broader perspective empowers researchers to devise effective strategies aimed at mitigating the repercussions of urbanization on the environment and human well-being, ultimately contributing to the enhancement of urban living conditions.

Enhancing outdoor thermal comfort

The quality of outdoor thermal comfort significantly influences the livability of urban areas. Changes in urban surfaces can substantially affect LST, consequently leading to elevated air temperatures and increased heat stress on urban residents (Lau et al. 2019 ). The LCZs framework proves to be a valuable tool in advancing research on outdoor thermal comfort by capturing the nuances of urban surface characteristics. For instance, Lau et al. ( 2019 ) employed a combination of questionnaires and field measurements to gauge subjective thermal sensations within eight distinct LCZs in Hong Kong. Unger et al. ( 2018 ) examined daily and seasonal fluctuations of outdoor human thermal perceptions, scrutinizing diverse LCZ types based on meteorological data. On a quantitative note, Liu et al. ( 2018 ) analytically assessed the levels of outdoor thermal comfort within nine LCZs in Shenzhen, dissecting the impact of various urban spatial characteristics. Schibuola and Tambani ( 2022 ) engaged in an evaluation of outdoor thermal comfort using the LCZs framework, offering a basis for comparative analysis of mitigation strategies. Meanwhile, Unal Cilek and Uslu ( 2022 ) analyzed the thermal conditions in urban green spaces across three distinct canopy cover scenarios using LCZs framework. Lastly, Wu et al. ( 2022 ) assessed the thermal comfort levels in Shenzhen throughout the year 2020 based on the LCZs framework.

These studies demonstrate that the LCZs framework enables a more profound comprehension of how urban surface characteristics affect outdoor thermal comfort. This understanding is crucial for developing and optimizing mitigation strategies in urban planning and design to enhance the quality of life and comfort for urban residents.

Tackling carbon emissions and building energy consumption

Cities play a significant role in global energy consumption and carbon dioxide emissions (Zhou 2022b ), making the development of sustainable urban areas pivotal for achieving climate stability objectives (Zhou 2023 , Zhou et al. 2023 ). The form and function of the built environment closely intertwine with its carbon emission patterns. Hence, the LCZs framework emerges as a valuable tool for research focused on mitigating carbon emissions and optimizing building energy efficiency. Through the creation of a regional carbon map grounded in the LCZs framework, researchers can furnish urban planners and decision-makers with crucial insights into urban carbon emissions, thereby bolstering strategic initiatives for carbon reduction and management.

Recent studies have harnessed the potential of the LCZs framework to scrutinize and chart building carbon emissions and energy utilization within urban landscapes. Notably, Wu et al. ( 2018 ) established correlations between building carbon emissions and LCZs classifications, culminating in a detailed mapping of LCZs-based building carbon emissions in Shanghai. This research enables a granular understanding of urban-scale carbon dynamics, essential for localized mitigation efforts. Additionally, Sharifi et al. ( 2018 ) introduced a novel LCZs-based urban carbon mapping method, offering a standardized approach to urban carbon assessment. This method found application in major global cities like Bangkok, Shanghai, and Tokyo, facilitating comprehensive carbon analysis. Moreover, the adaptability of the LCZs framework extends to energy consumption assessments for city-level energy management and planning. For instance, Yang et al. ( 2019b ) devised a diagnostic equation for daily maximum UHI indices grounded in the LCZs framework, effectively applying it to simulate building energy consumption. In a similar vein, Kotharkar et al. ( 2022 ) explored cooling loads and energy requisites for two distinct building typologies, leveraging the LCZs framework for insights into energy planning.

Collectively, these studies underscore the versatility and promise of the LCZs framework in guiding urban sustainability endeavors and informed energy planning, ultimately steering cities toward a greener, more energy-efficient future.

Limitations, challenges, and future prospects

Limitations and challenges.

While the LCZs framework presents a promising avenue for standardizing the exchange of global urban temperature data, its widespread adoption faces challenges due to the lack of a unified approach to data sourcing and LCZs classification, leading to inconsistencies in LCZs framework research. To ensure methodological consistency, it is essential to establish a standardized LCZs framework research protocol. The WUDAPT method, designed for data sharing and user-friendliness, shows promise for future urban climate studies based on LCZs mapping. However, a critical challenge remains in improving this method’s accuracy. Consequently, a key concern in LCZs research is developing a large-scale, effective, and precise LCZs mapping approach by leveraging various benchmark datasets and classifiers. This paper highlights current issues in the LCZs mapping process and suggests potential enhancements.

i) Data availability: Data availability poses significant challenges for LCZs mapping, stemming from several factors. These include limitations in the spatial and temporal resolution of RS data, difficulties in obtaining accurate and consistent ground truth data for calculating UCPs, the high cost associated with accessing high-quality RS data, etc. These challenges emphasize the need for a generalizable framework that addresses data availability issues. The WUDAPT team is actively working towards this goal and has curated a list of datasets for UCPs calculation, including building data, tree data, and urban population data, which can be accessed on the official website ( https://www.wudapt.org/third-party-data/ ).

ii) RS-based mapping: RS-based mapping predominantly relies on freely available Landsat satellite image data. However, the limited image resolution of Landsat data can compromise LCZs mapping accuracy. To mitigate this limitation, the use of low-cost and user-friendly unmanned aerial vehicles (UAVs) devices for high-resolution RS image capture is worth considering. This approach can mitigate the impact of weather conditions and cloud cover on images, ultimately enhancing the precision of training sample identification and LCZs classification.

iii) Training samples: The overall accuracy of the WUDAPT method depends on the precise identification of LCZ types within the training samples. However, challenges may arise during data collection and UCPs calculation due to limited professional knowledge among researchers, potentially leading to inaccurate LCZs identification. To mitigate these challenges, the accuracy of training sample recognition can be improved through the standardization of data collection and UCPs calculation processes. This will help reduce subjective errors and address expertise-related constraints that can hinder manual recognition.

iv) Classifier: Apart from training samples, the classifier’s ability to achieve high-precision LCZ type recognition is pivotal in LCZs mapping research. Recent advancements in artificial intelligence, particularly deep learning, have revolutionized image recognition and found widespread application in image classification tasks. Consequently, the emerging trend is to leverage neural network algorithms to achieve large-scale, efficient, and precise LCZs mapping.

By addressing these challenges and limitations, the LCZs framework can evolve into a more robust tool for urban climate research and planning, ensuring improved accuracy and consistency across studies.

Future prospects

The LCZs framework’s generality, simplicity, and objectivity make it remarkably versatile, positioning it for extensive application across various future research domains. Beyond its current role in UHI effect research, the framework exhibits potential for a plethora of other areas, such as urban design, outdoor thermal comfort, carbon emissions, building energy consumption. The trajectory of LCZs framework research can be delineated into the following directions:

i) Enhancing understanding of UHI: Previous studies evaluating UHI effects have predominantly relied on 2D planar analysis, which does not account for the 3D physical form of cities. The LCZs framework provides an avenue for 3D spatial analysis, facilitating a more comprehensive evaluation of UHII. This advancement can significantly enhance our understanding of UHI effects and foster the development of innovative UHI mitigation strategies.

ii) Urban design: The LCZs framework serves as a valuable tool for identifying climate risks within urban areas. Urban planners, government decision-makers, and stakeholders can leverage this framework to formulate plans for climate-sensitive urban development, thereby promoting the creation of sustainable and resilient cities. Through the utilization of the LCZs framework, these stakeholders can gain valuable insights into potential climate risks, enabling them to proactively implement measures that enhance the effectiveness and efficiency of urban planning and development.

iii) Exploring complex urban climates: While recent urban climate studies have started to consider the influence of complex geographical factors such as topography and water bodies, there remains a research gap concerning mountainous cities. These cities, characterized by unique topographical elements and complex urban climates, have received comparatively less research attention. Therefore, future urban climate research can delve into the analysis of urban climates in mountainous cities using the LCZs framework. By leveraging this framework, researchers can gain a deeper understanding of the intricate interactions between topographical features and urban climates in these unique settings.

iv) LCZs-based economic-environmental analysis: Economic-environmental analysis aids policymakers and businesses in harmonizing economic growth with environmental sustainability by quantifying the environmental impacts of economic activities (Zhou 2022a ). Future LCZs research can evolve towards economic-environmental analysis. The LCZs framework provides a foundational understanding of urban physical characteristics and functions, which can be correlated with economic activities and environmental impacts. Integrating economic analysis into LCZ studies, such as integrating lifecycle assessment methods to quantify the environmental impacts of various urban development scenarios, enables researchers to investigate the cost-effectiveness of diverse urban development strategies, evaluate the economic implications of carbon emission reduction, and assess the financial advantages of sustainable building practices.

These future research directions promise to further amplify the applicability and impact of the LCZs framework in urban climate studies, urban planning, economic activities, and climate-conscious urban development.

Conclusions

This study provides a systematic and critical overview of LCZs framework research, exploring its evolution, current status, and future prospects based on recent advancements. It underscores the LCZs classification system’s effectiveness in guiding climate-responsive planning and design. The study’s key contributions are summarized as follows:

1) The proliferation of publications on the LCZs framework has been remarkable, escalating from 17 in 2013 to 300 in 2022. This surge in research reflects a prominent trend towards interdisciplinary collaboration, with LCZs research encompassing ten primary categories, including meteorology atmospheric sciences, environmental sciences ecology, and physical sciences among others.

2) The ongoing challenge of achieving large-scale, efficient, and accurate LCZs mapping remains a central concern in LCZs research. Efforts to address this challenge have been underway, with researchers integrating diverse benchmark datasets, employing UAVs, and utilizing deep learning classifiers.

3) In the realm of UHI studies, the LCZs framework has demonstrated its suitability for 3D UHI analysis, enriching the comprehension of UHI dynamics and their repercussions on urban environments. Recent LCZs framework investigations have evolved from single-city analyses to comparative studies encompassing multiple cities. Moving forward, the LCZs framework holds promise for deciphering the complexities of urban climates influenced by intricate geographical factors.

4) For climate-responsive urban design, the LCZs framework serves as an invaluable instrument for devising strategies that prioritize climate sensitivity in urban planning and development. The integration of green and blue infrastructure, building design principles, and innovative street design emerges as fundamental elements in fostering climate-conscious cities through the LCZs framework.

5) The LCZs framework exhibits versatility across various research domains, including outdoor thermal comfort, carbon emissions analysis, and building energy consumption assessments. Its application contributes significantly to advancing ecological urban construction and promoting sustainable urban development.

In summation, the LCZs framework stands out as a powerful instrument with broad implications for urban climate research, urban planning, and the advancement of climate-resilient and sustainable cities. Its ongoing evolution and refinement are poised to catalyze innovation and advancements in these crucial domains.

Data availability

Data sharing is not applicable to this article as no new data were created or analyzed in this study.

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Acknowledgements

This work was supported by Innovation Project of Guangxi Graduate Education (YCSW2023306), Natural Science Foundation of Guangxi Province of China (No.2018GXNSFAA281212).

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Jie Han: Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Writing—original draft. Nan Mo: Conceptualization, Formal analysis, Investigation, Methodology, Writing—original draft. Jingyi Cai: Conceptualization, Formal analysis, Investigation, Methodology, Writing—review & editing. Leixin Ouyang: Conceptualization, Formal analysis, Investigation. Zhengxuan Liu: Conceptualization, Formal analysis, Investigation, Methodology, Supervision, Writing—original draft, Writing—review & editing.

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Han, J., Mo, N., Cai, J. et al. Advancing the local climate zones framework: a critical review of methodological progress, persisting challenges, and future research prospects. Humanit Soc Sci Commun 11 , 538 (2024). https://doi.org/10.1057/s41599-024-03072-8

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• 2 Veterinary Expert, Swansea, United Kingdom
• 3 School of Applied Sciences, London South Bank University, London, United Kingdom

Reptile expos are typically itinerant events at which live wild-caught and/or captive-bred turtles, tortoises, crocodiles, lizards, and snakes are displayed, sold, or exchanged for pet keeping purposes. We conducted a literature review and analysis of reports regarding animal welfare and public health issues of concern associated with the display and sale of reptiles at expos in Europe and North America. We also conducted a limited survey of several relevant government authorities to briefly appraise existing situations regarding governance and law internationally, and performed a further limited examination of online advertisements in order to estimate the number of events. In addition, we conducted an analysis comparing husbandry standards for reptile expos versus other animal display or sale situations using UK formal legal guidance, which adopts the Five Welfare Needs as a basis. Finally, we also conducted a SWOT (strengths, weaknesses, opportunities, and threats) analysis of key features associated with reptile expos. We identified at least 10 animal welfare and 5 public health and safety problems as occurring and endemic to the typical operation of reptile expos. Comparisons between the ways in which animal welfare and public health issues are regarded or managed for reptile expos in relation to, for example, traditional zoos, mobile zoos, and pet sales are stark and concerning, with expos constituting the least protective and potentially most harmful situations out of all captive reptile-keeping scenarios. The lack of monitoring and control of reptile expos, combined with their frequent occurrence, strongly indicates the requirement to urgently control and prohibit these events. We recommend that where reptile expos are already essentially prohibited such bans should be immutable and not subject to any weakening provisions. Where reptile expos are permitted and/or subject to limiting conditions, or where reptile expos are not subject to limiting conditions, then our recommended 40 stipulations and overarching control principles should be applied as interim mitigating measures pending the introduction of prohibitions or ‘bans’. Governments should aim to ensure that enforcement of such measures is robust.

1 Introduction

Reptile expos (also referred to as shows, markets, breeders’ meetings, or fairs) are typically itinerant events at which live wild-caught and/or captive-bred turtles, tortoises, crocodiles, lizards and snakes are displayed, sold, or exchanged for pet keeping purposes ( Arena et al., 2012 ; Altherr, 2014 ; Schoonover, 2019 ; D’Cruze et al., 2020 ; Warwick and Steedman, 2021 ). Whilst some entirely non-trade-related events may occasionally occur, reptile expos are frequently and largely commercial, although often portrayed as ‘hobbyist’ gatherings by some organisers in order to avoid trade-relevant laws ( Arena et al., 2012 ; Altherr, 2014 ; D’Cruze et al., 2020 ). There can be some similarity between reptile expos as characteristically observed in Europe and North America and wildlife markets that occur in, notably, Asia and South America. In particular, European and North American reptile expos almost exclusively sell animals for pets, whereas in Asia and South America, animals may be offered or acquired for purposes including human food, traditional local medicines, curio products, or pets ( Warwick and Steedman, 2021 ). Some expo events involve animal classes other than reptiles (e.g., invertebrates, fishes, amphibians, and mammals) and may be broadly described as featuring exotic animals ( Arena et al., 2012 ).

Reptile expos have raised several major and recurring concerns as expressed by non-governmental organisations as well as the scientific community, notably regarding poor animal welfare ( Arena et al., 2012 ; Altherr, 2014 ; D’Cruze et al., 2020 ), threats to public health and safety, from zoonotic infections ( Arena et al., 2012 ; Warwick et al., 2012b ; Warwick and Steedman, 2021 ), propagation of emergent disease spill overs ( Warwick and Steedman, 2021 ; Vora et al., 2023 ), introduction of invasive alien species ( Arena et al., 2012 ; Altherr, 2014 ; Warwick and Steedman, 2021 ), trading of threatened or endangered species ( Arena et al., 2012 ; Altherr, 2014 ; Nijman and Stoner, 2014 ; Auliya et al., 2016 ; Hruby, 2019 ; Altherr and Lameter, 2020 ; Das and Auliya, 2021 ), selling of wild-caught animals ( Arena et al., 2012 ; Altherr, 2014 ; Auliya et al., 2016 ; Altherr and Lameter, 2020 ), and misrepresentation of operational status to avoid legal controls ( Arena et al., 2012 ; Auliya et al., 2016 ). Relatedly, the overall ethics of trading and keeping of reptiles generally has also been challenged ( Warwick, 2014 ).

Reptiles are accepted to possess sentience, as well as the abilities to sense pain and stress ( Lambert et al., 2019 ; Learmonth, 2020 ; Arena et al., 2023 ; Font et al., 2023 ; Lillywhite, 2023 ); thus, as for other animals, they warrant concern for their welfare and life quality. Moreover, contrary to some perceptions, many if not most reptilian lifestyles manifest complex behavioural repertoires and psychological performances, including sociality, play, environmental awareness, self-awareness, sensory perception, and mental abilities to problem-solve and numerically count that frequently competes with or exceeds birds and mammals [e.g ( Burghardt, 1998 ; Manrod et al., 2008 ; Wilkinson and Huber, 2012 ; Burghardt, 2013 ; Szabo et al., 2021 ; Arena et al., 2023 ; Burghardt and Layne-Colon, 2023 ; Doody, 2023 ; Font et al., 2023 ; Gillingham and Clark, 2023 )]. However, although there is some overlap with other animal classes, reptilian biology and welfare is also strongly dominated by certain highly specialised features, notably ectothermy and thermoregulation, metabolic and energetic rate, innateness and ancestral traits, and nocturnality. Reptile expos involve environments that are notably deprived in respect of, for example, positive stimulation and habitat diversity, and also overly represented by negative stimulation, for example, severe spatial restriction and disturbances. These issues imply significant impacts on welfare and disfavourably weigh against any perceived strengths promoted for reptile expos, as further indicated in our SWOT analysis.

Reptilian life under natural conditions is complex, and whilst little is known regarding biological histories in the wild for most reptile species, no information is comprehensive for any reptile species ( Warwick et al., 2023a ). Importantly, as objective data regarding reptile biology in the wild is increasing, this knowledge confirms that these animals are highly evolved in terms of environmental, physiological, behavioural, and psychological developments and requirements ( Warwick et al., 2023a ). Below, we present very brief summary comparisons between selected features of natural biology for two reptile species that are commonly kept as pets, and which offers insight into some marked differences between wild versus captive lifestyles.

For example, bearded dragons ( Pogona vitticeps ) are members of the Agamid lizard family native to eastern and central Australia, and are one of the most commonly sold and kept pet reptiles, and frequently occur at reptile expos. Free-living bearded dragons occupy large home ranges of up to 45,000 m 2 , which involves diverse habitat types including desert, scrubland, and dry forest ( Craig et al., 2007 ). These lizards, which may reach approximately 60 cm in length, are opportunistic omnivores consuming a wide variety of invertebrates and vegetable matter, and occasional small mammals or reptiles ( Kubiak, 2020 ). Although not highly social, their behaviour is significantly hierarchical and territorial ( Oonincx et al., 2015 ; Kubiak, 2020 ). Formal government guidance for pet selling establishments in the UK advises spatial provisions of 4 x snout-to-vent length by 2.5 x snout-to-vent length as being suitable to house 2-3 adult lizards ( DEFRA, 2023b ). The formal guidance also stipulates suitability of environment, enrichment accessories to stimulate natural behaviour appropriate to the species, substrate, temperatures, humidity, light, water quality, ability to hide, and ability to bathe.

Corn snakes ( Pantherophis guttatus ) are members of the Colubrid family native to North America, and are one of the most commonly sold and kept pet reptiles. Free-living corn snakes occupy large home ranges of up to approximately 79,000 m 2 , which involve diverse habitat types including fields, trees, open habitat, and dry forest, and a range of altitudes to 1800 m ( Conant and Collins, 1991 ; Hedley and Eatwell, 2018 ). These snakes, which may reach approximately 150 – 180 cm in length, are carnivorous and ovivorous, feeding on a variety of herpetofauna, mammals and birds as well as birds’ eggs ( Conant and Collins, 1991 ; Rush et al., 2014 ). The snakes are largely solitary and crepuscular or nocturnal ( Conant and Collins, 1991 ). Formal government guidance for pet selling establishments in the UK advises spatial provisions of 2/3 x 1/3 snake length as being suitable housing ( DEFRA, 2023b ). The formal guidance also stipulates suitability of environment, enrichment accessories to stimulate natural behaviour appropriate to the species, substrate, temperatures, humidity, light, water quality, ability to hide, ability to bathe.

The examples above only minimally summarise factors relevant to life in the wild; thus far greater complexity can be assumed. Indeed, life under natural conditions may be regarded as being incalculably more complex than currently understood by science, which raises major questions regarding the extent to which the biological requirements of animals may be significantly under-appreciated and unmet at reptile expos.

Public health and safety issues associated with reptile keeping generally, which is relevant to expos, include risks of injury (such as bites, scratches, envenomations, associated infections and allergic reactions) ( de Haro and Pommier, 2003 ; Schaper et al., 2009 ; Warwick and Steedman, 2012 ). However, for this report we will focus on the public health issues of zoonoses, which are infections transmissible from animals (here reptiles) to humans, because little information appears to be available regarding injuries from animals to people. Approximately 200 zoonoses are known, and involve bacterial, viral, fungal, and parasitic pathogens ( Warwick et al., 2012a ). Despite the diversity of zoonotic agents linked to reptiles, Salmonella spp. constitute the most commonly reported infections ( Mermin et al., 2004 ; Zając et al., 2021 ), with approximately 70,000 occurring in the United States, and 6,000 in the United Kingdom annually ( Woodward et al., 1997 ; Mermin et al., 2004 ; Toland et al., 2012 ). Among more than 1,400 surveyed human diseases, over 60% have been identified as being of potentially zoonotic origin ( Karesh et al., 2005 ), and at least 40 are associated with reptiles ( Warwick et al., 2012a ). Also, among global emerging human diseases, 75% have a wild animal link ( Brown, 2004 ). Accordingly, based on the diversity of species involved and the accessibility of the public to these animals, their environments, and the probability of widespread contamination, reptile expos can be considered significant hubs of potential zoonotic infection.

The probable presence of atypical or exotic pathogens at reptile expos has been highlighted as an important concern ( Warwick et al., 2012a , b ; Zając et al., 2013 ). A recent large-scale study sampled 731 reptiles and their environments at exhibitions to determine the presence or otherwise of Salmonella ( Zając et al., 2021 ), and found Salmonella to be present in 92% of snakes, 84% of lizards, and 60% of turtles. Salmonella was also found in 82% of swabs from table and floor surfaced post reptile exhibition. In total, the study found 918 strains of Salmonella belonging to 207 serovars and serological variants, including types of high public health significance. Whilst there are relatively few case reports [e.g ( Weiss et al., 2011 )] of infection directly attributable to attendance at reptile expos, this situation is likely symptomatic of classic under-reporting due to habitual disassociation – infections occurring without determining a causal link, which is exacerbated by inadequate investigation of patients by health care professionals ( Warwick and Corning, 2013 ).

The global numbers of reptile expos are unknown. The number of reptiles presented at each event is variable, but it has been estimated that tens of thousands of animals may be displayed or sold at a single venue ( Hruby, 2019 ). A considerable diversity of animals is frequently available at reptile expos, and one study identified at least 148 species at three individual events across Spain, The Netherlands, and United Kingdom ( Arena et al., 2012 ). In some countries or regions, reptile expos that include a commercial nature are effectively prohibited (e.g., in UK), whereas in others they are either legally permitted (e.g., regions of Canada, the United States, Belgium, Germany, Spain, The Netherlands), or otherwise continue to manifest regardless of intended controls (e.g., UK, regions of the USA) ( Arena et al., 2012 ; Altherr, 2014 ; Auliya et al., 2016 ; Altherr and Lameter, 2020 ).

This report focuses on animal welfare, including relevant key biological factors, and public health and safety issues pertinent to expos in Europe (Belgium, Germany, Spain, The Netherlands, United Kingdom), and North America (Canada and the United States), which are known to host many examples, as well as some relevant management concerns. We also present examples of legislation and/or regulations and their ability or otherwise to control relevant problems associated with these events. In addition, we also present a SWOT (strengths, weaknesses, opportunities, and threats) analysis of key features associated with reptile expos. We aim to summarise the key characteristics of reptile expos as well as the concerns and problems associated with their operation. Finally, given the lack of objective guidance or controls pertaining to reptile expos, this report also aims to produce recommendations and stipulations that may be widely applied to the range of problematic issues using existing frameworks or where regulation is absent.

We conducted a literature search using the engines Scopus and Google Scholar ( Box 1 ) for peer-reviewed reports published between 2010 and present, with a view to collating, in particular but not exclusively, reported information and concerns regarding animal welfare, public health and safety, general management issues, and governance and law internationally. A number of reports were unavailable due to inaccessibility or irrelevant due to their peripheral nature as indicated by their titles or abstracts. Google Scholar also includes non-peer reviewed material and secondary sources, which contributed to the requirement for removal. Google Scholar searches for words that are contained anywhere in an article, which leads to identification of significant numbers of both relevant and irrelevant reports. Numerous reports were captured that constituted duplicates held within the authors’ own libraries and are effectively contained under the ‘removal of duplicates’ in Box 1 . Relevant reports were analysed by comprehensive examination to identify any cited concerns arising from reptile expos. Each concern was listed sequentially in a table, such as “lack of water” or “barren environment” along with its reference or source. When all papers had been analysed, similar concerns were grouped together and tabulated. Our literature review followed the guidelines for rapid reviews ( Khangura et al., 2012 ; Dobbins, 2017 ). From the literature review we identified and categorised reports regarding animal welfare and public health issues of concern associated with the display and sale of reptiles at expos.

Also, to briefly appraise existing regulations, we conducted (via email) a limited survey of several relevant government authorities in Europe (Belgium, Germany, Spain, The Netherlands, United Kingdom) (some regional data was further obtained from Germany and Spain on reference from national departments) and provincial/state government departments in North America (Canada and the United States). We sought information from relevant departments by describing the nature of reptile expos as: “Events of interest are those typically named or referred to as: reptile shows, reptile expos, reptile markets, reptile trade fairs, reptile fairs, reptile breeders’ meetings. These events characteristically include the display and sale of reptiles (whether wild-caught of captive-bred) by commercial or non-commercial entities. Events are usually itinerant, occur over one or two days, and may occur infrequently or regularly at venues accessible to the public” and asked the following questions: “ 1. How many, if any, of these events do you experience in your jurisdiction annually? 2. What, if any, formal or informal regulations do you have to manage animal welfare and public health and safety at these events?” We contacted 88 government authorities and received 43 responses. The survey was emailed to at least one relevant government authority in each country or region with a request to either supply contact information for, or forward the email to, a contact most able to answer the questions. Responses were summarised by documenting the numbers of events as estimated or known by each relevant authority, and whether or not an authority operated particular legislation, or issued guidance. We also performed a limited examination of online advertisements in order to estimate the number of events using Google (for Europe and Canada) and Opera (for US) search engines. The name of the region followed by ‘reptile expo’ was used to make each search and the number of relevant expos advertised collated from the first page-scroll, which included approximately 50-60 entries after which results were found to be of low relevance or repetitious. We also used the Five Welfare Needs model ( RSPCA, 2006 ) to analyse key comparisons regarding legal stipulations for animal husbandry, as well as public health and safety, at four display and sale situations. Finally, we also conducted a SWOT (strengths, weaknesses, opportunities, and threats) analysis of key features associated with reptile expos. Each key feature was itemised by reading all relevant reports and including any or all issues that were clearly identifiable within the remits of the four SWOT criteria. Strengths imply areas that work well or function, although these relate to factors that benefit organisers and attendees of expos. Manifestly, many people obtain some benefits, for example, financial or enjoyment. Weaknesses imply areas of under-performance or failure and that require change. Because weaknesses imply problems, they are also indirectly related to threats. Opportunities imply areas where improvements or changes can or should be made in order to ameliorate or resolve weaknesses and threats. Threats imply areas of actual or potential problems of concern, which in some respects also relates to weaknesses.

Box 1. Search results from Scopus and Google Scholar for reptile expos. *Due to the search algorithm in Google Scholar, the search identified many papers not all of which were relevant.

3.1 Animal welfare

Table 1 provides information from the published literature regarding animal welfare issues of concern associated with the display and sale of reptiles at expos. The body of evidence in the table presents both hazards and welfare consequences, and relates to housing, management, and behaviour, as well as health parameters of the animals.

Table 1 Documented concerns regarding reptile expos: animal welfare.

3.2 Public health and safety

Table 2 provides information regarding reported health and safety issues of concern associated with the display and sale of reptiles at expos. The table presents issues relevant to pathogens, contagious diseases, resistance to (veterinary/human) drugs/medicines, disease threats, and control measures.

Table 2 Documented concerns regarding reptile expos: public health.

3.3 Governance, law and number of events

In respect of our survey of government authorities, minimal responses were received from agencies. Most countries and regions have generalised animal protection regulations under which, theoretically, most or all captive situations fall, although these may not specifically relate to reptile expos but retain relevance. General legislation also applies to the movement, sale, and keeping of listed threatened, injurious, invasive, and, sometimes, native species in Europe and North America. Specific regional responses regarding number of events and applicable legislation are provided in Appendix 1 .

Amongst the responding governments the estimated numbers of reptile expos per region were up to: Europe n = 56, and North America n = 196 (Canada n = 15, US n = 181). Survey responses were received from 29 of 50 US States, 6 of 13 Canadian Provinces and Territories and 6 of 7 European countries. However, various government departments in any region may be involved in the regulation of expo type events depending on, for example, the individual species involved (e.g., native or non-native, invasive or not), importation regulations, or public health risks (e.g., large or venomous reptiles or zoonotic risks). Not all relevant departments were contactable via the email survey because some regions and/or government departments either do not have publicly accessible emails or block emails from out-of-country sources, leading to incomplete data. However, due to the incomplete responses received, variability of type of information provided by respondents, and challenges to standardisation, the information summarised below and in Appendix 1 should be regarded as offering only very approximate examples of legislative approaches or their absence regarding reptile expos, as well as the number of events occurring.

From limited examination of events advertised online, we identified that at least 61 reptile expos occur annually in Europe (Belgium n = 6, Germany n = 33, Spain n = 5, The Netherlands n = 15, United Kingdom (England) n = 2), and 163 reptile expos in North America (Canada n = 21, United States n = 142).

We also compared husbandry standards for reptile expos versus other animal display or sale situations using UK formal guidance ( DEFRA, 2023a ; DEFRA, 2023b ; UK Government, 2023c ) in relation to the Five Welfare Needs model ( Appendices 2A – E ). Our analysis identified no specific governmental guidance provisions for the welfare or management of reptiles at expos. In addition, we used English Government legal provisions ( DEFRA, 2023a ; DEFRA, 2023b ; UK Government, 2023c ) to provide comparative examples concerning legal stipulations for public health and safety regarding four different animal display or sale situations: static zoos; mobile zoos; pet retail or wholesale sellers; and reptile expos ( Appendices 3A – E ). Our analysis identified no specific governmental guidance provisions pertaining to public health and safety at expos.

3.4 SWOT analysis

Our SWOT (strengths, weaknesses, opportunities, and threats) analysis of reptile expos is provided in Box 2 below.

Box 2. SWOT (strengths, weaknesses, opportunities, and threats) analysis of reptile expos (no particular order).

4 Discussion

Animal welfare and public health issues are increasingly recognised as importantly integrated under the ‘one-health’ umbrella, which summarises a paradigm in which environment, animals, and people are interconnected ( Rabozzi et al., 2012 ; Cantas and Suer, 2014 ; Garcıá Pinillos, 2021 ; Broom, 2022 ; CDC, 2022 ). For example, chronically stressed animals may be more likely to shed potentially zoonotic and other cross-species infections that may negatively and diversely affect animals, people and ecologies. Relatedly, collection of wild animals for the pet trade can involve major disturbances to habitat ecologies and contribute to emergent diseases and pandemics ( García-Moreno, 2023 ). Therefore, reptile expos encompass a range of issues that collectively come under the one-health paradigm. Our investigation identified numerous specific animal welfare and public health and safety concerns, as well as general management concerns, associated with reptile expos. For our SWOT analysis ( Box 2 ) we drew together key aspects mentioned in the literature and categorised these according to strengths, weaknesses, opportunites, or threats, as implied in the test. Evidently, overall, far more areas were associated with problems than with benefits. Below, we further examine each of these concerns.

4.1 Animal welfare

The animal welfare concerns that we identified were, in particular: unenriched, barren, or deprived environments; absence of food or water; severe spatial restriction; crypto-overcrowding (inability for all animals to use any single provision at one time); animals held in accommodation designed as temporary, for prolonged periods of time; invasive disturbances: transportation, handling, sound, noise, vibration, light, and observation stress; psychological stress and abnormal behaviour; and injury and disease ( Table 1 ). Animal welfare issues also featured negatively within our SWOT analysis ( Box 2 ).

4.1.1 Unenriched, barren or deprived environments; absence of food or water; severe spatial restriction, crypto-overcrowding

Unenriched, depauperate and deprived environments are commonly present at reptile expos, for both solitary or multiple occupant situations, including inadequate or no provision or management for climate control within enclosures or opportunities for basking, severe restrictions regarding mobility, inadequate shelter, lack or absence of water and food, lighting, and humidity needs, insufficient or absent substrate, inadequate burrowing facilities, and poor hygiene ( Arena et al., 2012 ; D’Cruze et al., 2020 ), all of which are likely to cause stress ( Burghardt, 2013 ).

Figures 1 – 4 provide examples of typical husbandry conditions for a variety of reptiles at expos.

Figure 1 Tortoises in display/sale containers at Hamm, Germany. (Credit: Phillip Arena).

Figure 2 Gecko lizards in display/sale containers at Doncaster, UK. (Credit: Animal Protection Agency).

Figure 3 Juvenile snakes in display/sale containers at Hamm, Germany. (Credit: Phillip Arena).

Figure 4 Adult pythons in display/sale containers at Sabadell, Spain. (Credit: Phillip Arena).

The extremely restrictive spatial conditions affect most animals, in particular snakes, which are prevented from extending their bodies or engage in any locomotor movement ( Arena et al., 2012 ; D’Cruze et al., 2020 ). The overwhelming objective scientific research and guidance stipulates that snakes must be able to fully stretch in their enclosures as part of essential normal behaviour and health maintenance [e.g ( Warwick et al., 2018 , 2019 ; Spain et al., 2020 ; Hollandt et al., 2021 ; Warwick et al., 2021 ; Cargill et al., 2022 )]. A recent UK Government scientific review concluded that snakes should be able to fully stretch in all enclosures ( AWC, 2023 ). Relatedly, at least 20 problematic clinical and 24 behavioural issues have been identified with the use of such diminutive enclosures for snakes, which is also relevant to conditions typical at reptile expos ( Warwick et al., 2019 ; Arena and Warwick, 2023 ). Many other species, notably lizards, are also subject to severe spatial limitations at reptile expos, in which animals are incapable of fully extending their bodies (tip of snout to tip of tail) and freely moving around within their enclosures ( Arena et al., 2012 ). Indeed, most animals are effectively forcibly coiled within diminutive plastic tubs or boxes. Accordingly, spatially overly-restrictive containers and major restriction of movement are a considerable concern ( Arena et al., 2012 , 2023 ).

Long periods without food, water, or exercise (e.g., including inter-state or international travel to and from venues) ( Arena et al., 2012 ) are considered to constitute significant stressors, which may also become cumulative factors that negatively affect health ( Arena et al., 2012 , 2023 ; Mancera and Phillips, 2023 ; Warwick, 2023 ). Relatedly, crypto-overcrowding refers to situations where, regardless of available space, all animals cannot use any single provision at the same time ( Warwick et al., 2018 ; Warwick, 2023 ). For example, any enclosure that contains a water vessel or basking area that all animals cannot fully utilise together and simultaneously infers crypto-overcrowding. Thus, whilst spatial factors may superficially appear adequate, closer inspection can reveal an overcrowded situation. The inherent use of diminutive enclosures and minimalist provisions at reptile expos directly promotes crypto-overcrowding.

Relatedly, reptiles, being ectothermic, are highly dependent on precise environmental conditions to control their body temperature to within fractions of a degree Celsius using behavioural thermoregulation in order maintain homeostasis and the maintenance of normal physiological states, digestion, metabolism, physical activities, immunological condition, and other factors ( Frye, 1991 ; Arena et al., 2023 ; Gillingham and Clark, 2023 ; Lillywhite, 2023 ). Accordingly, highly complex captive conditions regarding artificial climate as well as habitat diversity are vital to promoting good health and welfare and avoiding harm in captive reptiles ( Burghardt and Layne-Colon, 2023 ; Greenberg, 2023 ; Mancera and Phillips, 2023 ; Mendyk and Augustine, 2023 ; Warwick and Steedman, 2023 ).

4.1.2 Prolonged and problematic ‘temporary’ accommodation; animals held in accommodation designed as temporary, for prolonged periods of time

The captive conditions referred to previously, may be argued to constitute temporary arrangements, and thus may not involve enduring stresses for animals. However, such situations, even in the course of a single day, are capable of causing significant and major stress in reptiles, with potentially lasting consequences, such as behavioural frustration, immunological compromise, opportunistic disease, and death ( Arena et al., 2012 ; Warwick, 2023 ; Warwick et al., 2023c ). Moreover, as discussed further below, allied to stressful conditions during the day(s) of display and/or sale, reptiles also frequently face extensive pre- or post-event stressors related to intensive breeding, transportation, handling (direct or indirect within containers or sacks), storage, and other issues ( Arena et al., 2012 ; D’Cruze et al., 2020 ; Warwick et al., 2023c ). Such cumulative stresses reasonably justify the need for even greater than normal relief than other situations; thus, the case can be clearly made that reptile expos have greater than normal obligations to provide enhanced conditions for rest and recovery for animals ( Gangloff and Greenberg, 2023 ; Warwick, 2023 ). Accordingly, a maximum period of 24 hours has been proposed to define short-term housing ( Warwick et al., 2023c ). While reptiles may experience captivity-stress under longer-term housing, such as general pet and hobby keeping and zoos, acute disturbances are particularly associated with expos.

4.1.3 Invasive disturbances; transportation, handling, sound, noise, vibration, light, and observation stress

The itinerant nature of reptile expos inherently involves the transportation of animals from holding sites to venues, encompassing handling, sound, noise, vibration, light, and observation stress ( Arena et al., 2012 ; Sollund, 2017 ; D’Cruze et al., 2020 ; Mancera and Phillips, 2023 ). Transportation is typically achieved by confining animals to diminutive containers or sacks, and travel periods can measure hours to days ( Arena et al., 2012 ). Such diminutive containers also frequently act as accommodation for the duration of expos, and then also for the return journey if unsold or onwards after sale, or to another venue, which may involve substantial transnational travel ( Arena et al., 2012 ; Sollund, 2017 ). Accordingly, reptiles may be confined to such conditions for several days, and static/supply base facilities can also be similarly minimalistic ( Arena et al., 2012 ; Sollund, 2017 ). Several welfare concerns regarding reptile expos relate to the issues of transportation conditions, the handling of animals and their containers by sellers as well as by many attendees ( Arena et al., 2012 ).

Consequently, reptiles may harbour significant stress burdens preceding, during, and after an expo, as have been identified through established specific behavioural indicators ( Martínez-Silvestre, 2014 ; Benn et al., 2019 ; Mancera and Phillips, 2023 ; Warwick et al., 2013a ; Warwick, 2023 ). These probable stress burdens infer that providing as comfortable conditions as possible for reptiles at expos warrant particular attention. In other transport and disturbance situations, following major confinement and transportation stresses, animals may be able to gain some degree of rest and recovery where promptly relocated to better conditions. However, for reptiles at expos, such potential respite is typically not available, which raises particularly serious welfare concerns.

Another issue associated with expos, disturbances and welfare monitoring is the matter of nocturnality among reptiles, which has implications for both invasive disturbances, as well as opportunities to assess the condition of animals. Many species of reptile are nocturnal, and thus are typically active during the night, morning, or evening. Nocturnality strongly conflicts with normal human activity patterns. This conflict implies that human disturbances to animals (caused by noise, vibration, light, and general movement within the environment), may significantly and negatively impact the normal resting periods of reptiles ( Mancera and Phillips, 2023 ; Warwick, 2023 ). Also, observation of animals, especially, during their normal activity periods, is important in order for caretakers to assess emergent welfare issues ( Warwick et al., 2018 ; Arena and Warwick, 2023 ; Warwick, 2023 ). It is probable that caretakers do not sufficiently observe nocturnal reptiles for potential welfare issues ( Warwick et al., 2018 ; Arena and Warwick, 2023 ).

4.1.4 Psychological stress and abnormal behaviour

Psychological stress and abnormal behaviour are well documented for captive reptiles, including at expos ( Arena et al., 2012 ; Warwick et al., 2013a ; Grant et al., 2017 ; Benn et al., 2019 ; Warwick, 2023 ). A study of 1,533 amphibians and reptiles displayed and sold at pet expos in Spain, The Netherlands, and the United Kingdom found that the prevalence of stress-related behaviour was as follows: interaction with transparent boundary 27.5%; hyperactivity 11%; hyper alertness 1.8%; rapid body movement 2.1%; flattened body posture 2.4%; head-hiding 4.6%; inflation of the body 0.5%; other significant signs (e.g., rostral lesion) 1.0% ( Arena et al., 2012 ). Given that observation periods for behaviour during the study were set at one minute, these findings indicate that stress-related behaviour is highly prevalent at reptile expos. Innateness is a significant factor related to aetiology of psychological stress and abnormal behaviour in reptiles. Innateness infers the presence of evolved ancestral, hard-wired, traits and drives that involve genetically programmed behavioural and psychological needs, such as long-distance and complex exploratory locomotor and transient activity, spatial and habitat expectations, prey acquisition, elective social interactions, and other factors ( Gillingham and Clark, 2023 ; Warwick, 2023 ). Accordingly, reptilian life is adapted to involve these highly programmed features (i.e., to behave and mentally function in natural contexts), which means that in captivity, without their provision, a raft of stress-related behavioural and mental problems occurs due to inherent inabilities to adapt ( Warwick, 2023 ). Within captive conditions numerous stress-related behavioural and mental problems are linked to conflicts between innate drives and depauperate environments ( Arena et al., 2023 ; Warwick, 2023 ). Accordingly, causes of psychological stress and abnormal behaviour can be multifactorial, and include inappropriate habitats, inadequate space, imbalanced social structures, and extraneous disturbances.

The above issues are diverse in nature and frequently associated with reptile expos in the literature. However, within our SWOT analysis ( Box 2 ) all these issues can be considered to fall within the criterion of ‘Animal welfare’ as presented under ‘Threats’.

4.1.5 Injury and disease

Injuries and disease among animals at reptile expos raise important concerns. Overly restrictive and inappropriate habitats, overcrowding, crypto-overcrowding, invasive disturbances, and behavioural drivers can each promote exploratory and escape activities in reptiles, which are typically frustrated due to confinement. However, such exploratory and escape activities can lead to physical injuries such as rostral abrasions, injured digits and tails, and aggression, all of which may further invite infection ( Frye, 1991 ; Warwick et al., 2013a ). Captivity-stress generally can also increase risks of succumbing to opportunistic infection ( Frye, 1991 ). Reptiles generally have relatively low metabolic and energetic rates; for example, energy expenditure may be approximately 2 - 5% of that compared to similar sized birds and mammals ( Nagy, 2005 ; Donoghue, 2006 ). Such low rates can have special significance regarding welfare in that the delayed onset of disease and the associated lag-phases regarding signs may obscure identifiable illnesses and their original causes, and complicate health assessment or remediation ( Frye, 1991 ). Water and food are often not provided for animals at reptile expos. While the energy and nutritional requirements for reptiles may be relatively low compared with, for example, many birds and mammals, and thus a lower required frequency of sustenance, small reptiles (whether juveniles or diminutive species) may still require frequent nutrition ( Lillywhite, 2023 ). Thus, reptiles may misleadingly appear normal at observation, yet also be experiencing degeneration, latent disease and poor welfare ( Frye, 1991 ). Thus, under-reporting of disease prevalence associated with reptile expos may be assumed. However, some cases of morbidity and mortality in reptiles have been linked to their acquisition at expos. For example, stress-related mortality was reported for a veiled chameleon ( Chamaeleo calyptratus ) ( Borza et al., 2012 ), fatal mycobacteriosis was recorded in a sand boa ( Eryx colubrinus loveridgei ) recently acquired at a reptile show ( Vetere et al., 2022 ), and pentastome infestation in a banded water snake ( Nerodia fasciata ) recently acquired at a reptile show ( Farrell et al., 2023 ).

4.2 Public health and safety

The public health and safety concerns that we identified, association with reptile expos were, in particular: probable presence of atypical/exotic zoonotic pathogens; probable presence of antimicrobial-resistant pathogens; contact with animals and their environments, dispersal of pathogens; poor or no hygiene control; and potential pandemic threats ( Table 2 ). As with other subjects examined during our SWOT analysis ( Box 2 ), public health and safety concerns dominated the weaknesses and threats elements of the text and appear to outweigh the potential human benefits offered by reptile expos.

4.2.1 Contact with animals and their environments, and pathogen dispersal

Handling of animals and contact with their environments are routine features of reptile expos ( Arena et al., 2012 ; Warwick et al., 2012a , b ; D’Cruze et al., 2020 ). The high prevalence of pathogens (notably, but not exclusively, Salmonella spp.) in reptiles implies strong risks regarding the presence of contamination in animals and their environments (e.g., enclosures, sellers, table surfaces, display paraphernalia), and thence to humans and their own items (e.g., clothes, carried items). Such prevalent contamination risks microbial transfer and disease in handlers, and also implies probable dispersal of contaminants to others and the wider environment ( Warwick et al., 2012a , b ; Zając et al., 2021 ). For example, an observational study of 813 attendees at three reptile expos found that 3.6% had direct contact with an animal and 27.3% had indirect contact with a presumed contaminated source, ( Warwick et al., 2012b ) within 5 minutes. Also, 18.7% of people made contact in respect of hand-to-mouth, 52.2% hand-to-body, and 19.9% person-to-person ( Warwick et al., 2012b ). Accordingly, behaviour at reptile expos frequently involves potential or probable contaminated contact episodes to own mouth, hair, clothes, and pockets; person-to-person contact.

4.2.2 Poor or no hygiene control; antimicrobial resistance; probable presence of atypical/exotic zoonotic pathogens

Reptile expos involve inherent challenges to control microbial transfer associated with direct contacts and subsequent re-contamination ( Warwick et al., 2012a , b ; Zając et al., 2021 ). Regular cleaning of surfaces is not typically practiced; thus, there is little or no control of fomites ( Warwick et al., 2012a , b ). Information provided (if any) regarding hygiene control at venues and at point of sale or hand over is also poor, minimalist, or absent ( Warwick et al., 2012a , b ; Zając et al., 2021 ). When provided, hygiene advice is typically limited to very low-key guidance regarding voluntary hand-washing ( Warwick et al., 2012a , b ; Zając et al., 2021 ), which may be offered to avoid dissuading people from acquiring animals. Hand-washing, whilst recommended, has limited benefits for prevention and control of infections such as salmonellosis ( Warwick et al., 2012a , b ). Also, the fact that many people touch, for example, their own hair, clothes, or pockets (thus transferring and storing microbes into those areas), implies that even if such measures as hand hygiene were practiced, occult recontamination is likely, and difficult to control ( Warwick et al., 2012a , b ).

Antimicrobial resistance is a major and growing global concern ( WHO, 2016 ). A study of reptile faecal samples conducted at pet stores, and private homes, as well as via fomite swabs at reptile exhibitions post-event in Poland identified contamination with atypical and drug-resistant Salmonella lineages ( S. kentucky ), and concluded that potential horizontal transfer of microbes may be facilitated by trade and exhibition practices ( Zając et al., 2013 ). Accordingly, the authors cautioned that in particular carnivorous reptiles (which consume diverse animal-based microbiomes) should be regarded as vectors for multi-drug-resistant infections ( Zając et al., 2013 , 2021 ).

4.2.3 Potential pandemic threats

Since 1919 there have been at least 19 major global pandemics associated with wildlife resulting in over 600 million human (excluding Covid-19) and countless animal deaths worldwide ( Warwick and Steedman, 2021 ). Wildlife markets are frequently implicated in these data, and generally are regarded to constitute significant risks as sources of emergent pandemic diseases ( Can et al., 2019 ; Kolby, 2020 ; Vora et al., 2023 ), and reptile expos have been categorised alongside these sources ( Arena et al., 2012 ; Warwick, 2020a ; Warwick and Steedman, 2021 ). In addition to being carriers of many bacterial and other pathogens, reptiles are also potentially capable of acting as incidental vectors for important viral agents via ingested prey ( Warwick and Steedman, 2021 ). Few or no quarantine or other importation control are imposed on reptiles because, as ectotherms, they do not transmit certain notifiable pathogens, such as rabies and some agricultural diseases ( Warwick and Steedman, 2021 ). The nature of trading in and keeping of reptiles can frequently involve the wild capture, transport and delivery of animals into commercial hubs and private homes within periods as minimal as approximately 24 hrs ( Warwick and Steedman, 2021 ).

4.3 General management concerns

The general management concerns that we identified in association with reptile expos were lack of veterinary supervision; miseducation, deficient knowledge-bases and impulse purchases; and threats to biodiversity conservation ( Table 1 ). Within our SWOT analysis ( Box 2 ), several problematic weaknesses and threats relate to general management at reptile expos. Individually and cumulatively, these concerns strongly account for the weaknesses and threats identified during our SWOT analysis.

4.3.1 Lack of veterinary supervision

Veterinary supervision to ascertain the health and welfare of animals kept in a variety of situations is widely integral to whether or not they (individual animals or entire collections) can be displayed or sold ( Warwick et al., 2013b , 2018 ). Broadly, veterinarians hold an overriding duty of care to safeguarding welfare and, accordingly, to assessing the state of each animal as well as reporting honestly regarding its condition ( Warwick et al., 2013b ). However, significant issues are inherent to reptile expos that severely complicate or negate the ability of veterinarians to perform normal inspection duties. To be effective, normal veterinary inspections require detailed examination of individual animals, or at least allow inspectors reasonable assessment enabled by accessibility and ease of observation. Reptile expos frequently involve thousands of animals and the inspecting veterinary team may be very small or even a single individual. Relatedly, many animals are confined in containers with highly limited access, meaning that normal conditions of veterinary inspection are greatly inhibited or impossible. In order to perform reliable and honest examinations and welfare assessments of animals, a high ratio of inspectors to animals would be required so that the health state of all animals could be ascertained prior to the commencement of any reptile expo. Veterinarians declaring animals fit for display and failing to conduct proper health and welfare assessments may constitute false declarations according to relevant codes of conduct, and potentially involve serious repercussions for attending inspectors.

4.3.2 Miseducation, deficient knowledge-bases and impulse purchases

Reptile expos are known to be associated with poor knowledge among exhibitors and sellers of animals, misleading education, poor husbandry, and encouragement of impulse purchases ( Arena et al., 2012 ; D’Cruze et al., 2020 ). Lack of knowledge and the perpetuation of false or misleading information handed down from keeper to keeper (so-called ‘folklore husbandry’) among those displaying or selling and keeping animals is an increasingly reported concern, with major welfare implications [e.g ( Arbuckle, 2013 ; Williams and Jackson, 2016 ; Arena et al., 2023 ; Jessop et al., 2023 ; Mendyk and Warwick, 2023 )]. Poor husbandry information prior to sale may encourage impulse purchases, and at point of sale or hand over lead to problematic care, animal welfare issues, and unwanted animals ( Warwick et al., 2014 ). Poor information, combined with evolved biological requirements and adaptive limitations, has resulted in widespread recognition that reptiles frequently experience poor care. For example, a six-year study of reptile mortality in the home in the UK found that 75% of reptiles do not survive one year ( Toland et al., 2012 ). Another study of snakes in the home found a mortality rate of 52% in 2 years ( Cargill et al., 2022 ). A study at a commercial seller warehouse in the USA found a mortality rate of 42% in 10 days (testudines, lacertilians, serpents) ( Ashley et al., 2014 ). Whilst tools are available to help would-be keepers make informed decisions regarding whether or not to undertake a pet reptile [e.g ( Warwick et al., 2014 ; Jessop et al., 2023 )], uptake of (notably scientific) guidance is also frequently lacking or poor ( Howell et al., 2020 ; Azevedo et al., 2021 ; Howell et al., 2022 ; Mendyk and Warwick, 2023 ).

Another factor that must be considered, is what care the animals will receive in their new homes. Reptile expos encourage impulse buys, sellers may not discriminate to whom they sell, and present examples of poor husbandry that may then be followed, along with the misconception that these are low maintenance pets ( Warwick et al., 2014 ). In addition, inadequate or misleading information is frequently contained in husbandry ‘care sheets’ that are offered ( Arena et al., 2012 ). Accordingly, the question of the welfare of the animals going forward is worthy of consideration. Although Crisante et al. (2023) found that owners of reptiles were more aware of their cognitive complexity and specialised requirements than non-owners, welfare problems in captivity persist, as documented, and can be caused in part by a lack of information and knowledge of how to meet these specialised needs. Research into how reptile expos encourage impulse buys by inexperienced owners and the extent to which they bear responsibility for providing accurate information on the complex needs of reptiles would be an interesting area for future research.

4.3.3 Threats to biodiversity conservation

Many reptiles sold by a variety of sellers are harvested from the wild ( Böhm et al., 2013 ). The lack of regulation of the global reptile trade has caused significant declines and threats to very many species ( Böhm et al., 2013 ). Despite regulatory mechanisms, such as the Convention on International Trade in Endangered Species (CITES) and other mechanisms, the illicit trade in reptiles is one of the largest illegal businesses in the world, with traders frequently ignoring regulations ( Marshall et al., 2020 ). The effects of this issue are twofold – depletion of species in the wild, possibly leading to them becoming critically endangered or extinct ( Marshall et al., 2020 ), and other species becoming invasive (for example the red-eared slider ( Trachemys scripta elegans ) has become globally invasive as a result of the pet trade ( Espindola et al., 2022 )). Reptile expos certainly contribute to this illegal trade and its associated issues, being a minimally regulated way for smugglers to sell reptiles ( Arena et al., 2012 ).

4.4 Governance, law and number of events

Based on the minimal responses to our survey of governments in Europe and North America ( Appendix 1 ), incomplete data and very few controls were identified for reptile expos. Accordingly, from the survey, it was not possible to offer precise figures of scale for reptile expos in Europe or North America. However, the estimates provided by responding governments for the numbers of reptile expos (Europe n = 56, North America n = 196) were not widely different from the numbers of events identified via our limited online survey of advertisements (for Europe and 61 for North America n = 163). In the US alone, it has been estimated that at least 300 itinerant animal events of various configurations, including reptile expos, occur annually ( Collis and Fenili, 2011 ). Our survey of government authorities was limited to selected regions and countries where reptile expos are popular, although many other countries also host these events ( Warwick and Steedman, 2021 ); thus, the reach of this survey was incomplete. Several regional US governments (Alaska, Arizona, Iowa, Mississippi) were unaware of events within relevant jurisdictions, despite their occurrence. Therefore, it appears that there is some disconnect between formal knowledge of reptile expos and actual occurrence of these events. This disconnect emphasises the need for recognition and control of reptile expos in all relevant regions. During our SWOT analysis, problematic weaknesses as well as several opportunities regarding control were identified. Later, we provide detailed protocols for the control of reptile expos.

4.4.1 Comparing husbandry standards for reptile expos versus other animal display or sale situations

Comparing formal stipulations for husbandry between different animal use sectors provides insight into the proposed standards of animal care, which has implications for welfare. The information provided in Appendices 2A–E and Appendices 3A–E includes English Government legal provisions (slightly edited for conciseness) to provide comparative examples concerning legal stipulations for animal husbandry regarding four different animal display or sale situations. These situations were static zoos; mobile zoos (categorised in England as animals for exhibition); retail or wholesale sellers; and reptile expos. In the UK all relevant animals are protected under the provisions of the Animal Welfare Act (2006) ( UK Government, 2023a ), which adopts the principles of the Five Welfare Needs, and relevantly relates to the Pet Animals Act 1951 ( UK Government, 2023b ).

Combined, these comparisons show that there is a dearth or absence of regulation or guidance for reptile expos compared with other animal activities. Essentially, beyond the elementary provisions of the UK Animal Welfare Act (2006) ( UK Government, 2023a ), there are no stipulations or other guidance specific to reptile expos. Sanctuaries or rescue centres would also add comparison to this discussion; however, there are currently no specific relevant legal guidance provisions in England, although a dedicated Bill may be under consideration ( UK Parliament, 2001 ). Furthermore, the operating practices that are typically associated with reptile expos (and that result in the welfare concerns presented in Table 1 ) are inferior to and incapable of meeting husbandry provisions that are normally required for the display or sale of animals in other situations or the primary provisions of, for example, the Animal Welfare Act (2006) in England and Wales. Relatedly, because of the itinerant operational nature of expos as well as the large volumes of animals and people involved, extraordinary additional measures are required in order to mitigate relevant risks to animal welfare and public health and safety.

Current practices endemic to reptile expos may be most likened to wholesale or retail pet sellers in that they typically display and sell animals (albeit from market table tops rather than static stores) and to mobile zoos and related itinerant exhibitions in that they exhibit animals and allow their casual observation and handling. Whilst reptile expos fail to even approximately meet the relatively detailed provisions designed for retail pet sellers, expos also grossly fail to meet the broad guidance designed for mobile zoos and related itinerant exhibitions. Guidance provisions for static zoos have some peripheral relevance, in that zoos are generally required to adopt foundational scientific principles and provisions rather than itemised guidance ( EAZA, 2022 ). However, in the UK, more specific husbandry guidance for zoos is currently in preparation and anticipated for publication in 2024. In the UK, current guidance for sanctuaries is relevant only to Scotland. Guidance for England and Wales is still being formally developed, thus comparisons cannot at this stage be made.

4.4.2 Development of new recommendations and stipulations

In Table 3 we provide evidence-based safety-net recommendations for managing reptiles at expos in situations where such events are either currently permitted or where immediate controls are necessary to mitigate inherent animal welfare and public health problems, pending stricter measures. Included are key provisions derived from established legislative requirements set out for static zoos, mobile zoos, and wholesale and retail centres, which are conveyed elsewhere (i.e., in Appendices 2A–E ). However, below we highlight some general points that provide context to recommendations contained in Table 3 . As indicated previously, husbandry conditions at reptile expos typically fall substantially below those of the general pet selling community, which has in itself been highly criticised for poor practices [e.g ( Ashley et al., 2014 ; Warwick, 2014 ; Mendyk, 2018 ; Whitehead, 2018 )]. Given the considerable risks to welfare and public health associated with reptile expos, selling or displaying animals in this way should not be allowed. However, this table can provide guidance on how to minimise risks wherever possible. Stipulations for control of reptile expos could be implemented in various ways, for example, via national, regional, or local governmental provisions or specific conditions attached to private venues by individual managers.

Table 3 Stipulations for control of reptile expos based on published scientific guidance.

4.4.3 Best practice standards

The term ‘best practice’ is widely used for animal husbandry recommendations and stipulations, but its meaning is highly contextualised. For example, within the high-level zoo community, best practice may infer large and complex habitats [e.g ( EAZA, 2022 ; UK Government, 2023c )]. In contrast, within the context of pet selling and keeping, the term is used more restrictively to infer substantially smaller and less complex environments [e.g ( DEFRA, 2023b )]. However, such differences should not be taken to imply that the lower standard best practice conditions for pets are scientifically or ethically acceptable; rather that for sellers and private keepers of reptiles, an overall lower standard of husbandry is typically expected. Accordingly, here, best practice implies conditions for animals that are also consistent within the context of selling and privately keeping pet reptiles.

Best practice standards infer the requirement that at all times caretakers of reptiles for expos significantly exceed the conditions stipulated below for absolute minimum standards in order to conform to legally and ethically defensible husbandry. Significantly exceeding absolute minimum standard conditions implies, for example: spatial provisions that enable snakes to freely move rectilinearly (fully stretched posture) in all dimensions within an enclosure; to bask and warm their bodies whilst in this posture under a broad heat source; for startled lizards to be able to accelerate, decelerate and stop without impacting confining barriers or to be able to drop from a height onto deep substrate or water; for turtles to be able to swim freely without having to contact co-occupants; and to burrow entirely within substrates. At its least, best practice should infer husbandry conditions similar to those expected for reptiles within the private home environment.

5 Conclusions

Reptiles are sentient animals with the abilities to sense pain and stress. Accordingly, welfare needs at reptile expos can be reliably presumed to be notably unmet. Despite highly incomplete formal information regarding the prevalence of reptile expos, these events occur regularly and widely within Europe, North America, and elsewhere. No government reported maintaining accurate records of reptile expos and their activities. There is very little specific monitoring or control of reptile expos, which is concerning given the breadth of significantly problematic issues endemic to their operation.

Exotic pet trading and keeping, which is a component of the wildlife trade in general, is increasingly scrutinised and criticised in scientific, legal, and ethical literature, for reasons of animal welfare, species conservation, protection of indigenous ecologies, and public health and safety. Reptile expos arguably represent one of the most problematic and uncontrolled sectors of the wildlife industry, with implications for all the aforementioned issues, which emboldens our rationalisation for regulation by way of bans.

This study identified numerous persistent and major animal welfare and public health and safety problems as occurring and endemic to the typical operation of reptile expos. Comparisons between the ways in which animal welfare and public health issues are regarded or managed for reptile expos in relation to, for example, traditional zoos, mobile zoos, and pet sales in the UK are stark and concerning, with expos constituting the least protective and potentially most harmful situations.

In order to alleviate historical and growing concerns regarding both animal welfare and public health and safety issues associated with reptile expos, we have developed two general recommendations based on our assessment of current control deficiencies, as well as 40 specific stipulations and overarching control principles derived from existing evidence-based guidance literature that are all designed to operate in unison and without selectivity. The underlying concepts and principles for these recommendations are that reptile expos currently cannot be assured to meet accepted best practice (and many lower) stipulations that are in place for other relevant events, and, thus prohibitions on their occurrence should be imposed where feasible. However, whilst prohibitions remain the key target, we adopt the pragmatic position that mitigating measures may be rapidly applied as interim measures pending pursuit of stronger legislative controls to protect animal welfare, public health, and other factors. Moreover, the recommendations we provide are all consistent with conventional minimum requirements established for the display or sale of reptiles; thus, they do not represent unreasonable provisions.

6 Recommendations

1. In situations where reptile expos are already essentially prohibited such bans should be immutable and not subject to any weakening provisions. Such actions are necessary because even robust permissive control measures will be unlikely to resolve the areas of concern raised in this report. In prohibiting reptile expos governments should aim to ensure that enforcement of such bans is robust. This recommendation is to ensure that the various risks associated with reptile expos are acted on comprehensively and preventatively.

2. In situations where reptile expos are subject to permissions and/or limiting conditions, or where reptile expos are not subject to permissions and/or limiting conditions, then the recommended 40 safety-net stipulations and overarching control principles that we provide in Table 3 should be applied as interim mitigating measures pending the introduction of prohibitions or ‘bans’. The 40 safety-net stipulations and overarching control principles are designed to operate in unison and without selectivity. In applying interim mitigating measures to reptile expos governments should aim to ensure that enforcement of all stipulations is robust. This recommendation is to ensure that absolute minimal ‘safety net’ conditions are met pending greater controls.

Author contributions

CW: Conceptualization, Funding acquisition, Investigation, Methodology, Supervision, Writing – original draft, Writing – review & editing. CS: Investigation, Writing – review & editing. MJ: Writing – review & editing. RG: Conceptualization, Investigation, Methodology, Writing – review & editing.

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This project was funded equally by the Animal Protection Agency (UK), Freedom for Animals (UK), World Animal Protection (UK, Netherlands, and Canada), and Zoocheck (Canada), which had no input regarding design, analysis, conclusions, recommendations, or other directional role in this report.

Acknowledgments

We are grateful to Dr Vanessa Cadenas Valdivielso for assistance with data collection in Spain, and to all governmental officials who assisted to provide relevant information. We are also most grateful to the reviewers and the Guest Associate Editor for their many constructive comments and suggestions.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fanim.2024.1335982/full#supplementary-material

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Keywords: reptile expo, reptile show, exotic pet market, animal welfare, zoonoses, public health, government control, government legislation

Citation: Warwick C, Steedman C, Jessop M and Grant R (2024) Reptile expos: an analysis and recommendations for control. Front. Anim. Sci. 5:1335982. doi: 10.3389/fanim.2024.1335982

Received: 09 November 2023; Accepted: 25 March 2024; Published: 30 April 2024.

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Copyright © 2024 Warwick, Steedman, Jessop and Grant. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Clifford Warwick, [email protected]