What is a Literature Review? Definition, Types and Examples

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Contents

• What Is a Literature Review?
• What a Literature Review Is NOT
• Why Is a Literature Review Important?
• Types of Literature Reviews
• A Closer Look at the Most Common Types
• How to Search the Literature: A Step-by-Step Guide
• How to Synthesize the Literature
• Literature Review for a Thesis or Dissertation: Special Considerations
• How to Structure a Standalone Literature Review Article
• References

A literature review is one of the most fundamental components of academic research and one of the most misunderstood. Whether you are writing a thesis, preparing a journal article, or beginning a new research project, mastering the literature review is essential. This guide covers everything you need to know: what a literature review is, how to search and synthesize the literature, the different types, and how to structure one effectively.

What Is a Literature Review?

A literature review is a critical analysis and synthesis of existing published material on a particular topic. It does more than simply summarize sources; it evaluates and connects them, drawing out themes, contradictions, methodological strengths and weaknesses, and gaps in current knowledge.

In the words of the University of Toronto’s Writing Advice centre, a literature review conveys “what knowledge and ideas have been established on a topic, and what their strengths and weaknesses are.” It must be defined by a guiding concept) your research objective, research question, or argumentative thesis) rather than being a descriptive list of materials.

What a Literature Review Is NOT

It is equally important to understand what a literature review is not:

• Not an annotated bibliography: an annotated bibliography summarizes each source individually with no synthesis between them
• Not an essay or research paper: it does not prove or develop a central argument from scratch
• Not a list of summaries: it goes beyond “Source A says X, Source B says Y”
• Not a report: it does not present findings from primary data collection

Why Is a Literature Review Important?

A well-conducted literature review serves multiple interconnected purposes:

Purpose	Description
Contextualises the research	Places your study within the existing body of knowledge
Identifies knowledge gaps	Highlights where research is absent, contradictory, or limited
Establishes credibility	Demonstrates your familiarity with the field
Informs theory and methods	Helps justify your theoretical framework and methodological choices
Guides research questions	Shapes and sharpens what you choose to investigate
Avoids duplication	Ensures your work builds on, rather than repeats, prior studies
Informs practice	For practitioners, review articles offer state-of-the-art evidence to guide decisions

Types of Literature Reviews

Not all literature reviews are the same. The type you choose depends on your research goals, your field, and the nature of the question you are investigating.

Type	Core Purpose	Approach	Best Used When
Narrative Review	Summarize and synthesize a broad topic	Flexible, thematic, qualitative	Providing background context; exploring a broad topic
Systematic Review	Answer a specific question with minimal bias	Highly structured, protocol-driven, exhaustive search	Aggregating evidence for evidence-based practice
Meta-Analysis	Statistically combine results from multiple studies	Quantitative synthesis using statistical methods	Sufficient homogeneous studies exist
Scoping Review	Map the extent and nature of a topic area	Comprehensive but exploratory	Emerging topics; assessing feasibility of a full systematic review
Descriptive/Mapping Review	Identify patterns and trends in the literature	Systematic search + frequency analysis	Understanding publication trends in a field
Critical Review	Critically evaluate and interpret existing literature	Reflective, appraisal-focused	Identifying methodological weaknesses in a body of work
Realist Review	Understand how and why complex interventions work	Theory-driven, context-sensitive	Complex social or policy interventions
Umbrella Review	Synthesize findings from multiple systematic reviews	Tertiary synthesis	Broad research topics with multiple existing systematic reviews

A Closer Look at the Most Common Types

Narrative Reviews

Narrative reviews are the most traditional form. They offer flexibility in how sources are searched and synthesized, and are particularly useful for providing context in research papers or introducing students and practitioners to a topic. However, they can be subjective if not carefully conducted.

Systematic Reviews

Systematic reviews apply explicit, reproducible methods to minimize bias. They typically require a pre-registered protocol, multiple independent reviewers, and exhaustive database searches. They are the gold standard in health and medical research.

Scoping Reviews

Scoping reviews are ideal when a topic is emerging or when you want to assess how much literature exists before committing to a full systematic review. They include grey literature and aim to be as comprehensive as possible.

Meta-analyses

A meta-analysis statistically combines data from multiple studies to generate a pooled effect size, providing more precise estimates of relationships or intervention effects than any single study can offer.

How to Search the Literature: A Step-by-Step Guide

Effective literature searching is a skill. A poorly executed search can leave crucial sources undiscovered or flood you with irrelevant material. Follow these steps systematically.

Step 1: Define Your Research Question

Before searching, you need a clearly formulated question. A well-articulated research question guides the entire review process: it determines which databases to search, which terms to use, and what inclusion criteria to apply.

Consider using a framework like PICO (Population, Intervention, Comparison, Outcome) for clinical questions, or PEO (Population, Exposure, Outcome) for other fields, to sharpen your question.

Step 2: Choose Your Databases

Different fields have different key databases. Use multiple databases to maximize coverage:

Field	Recommended Databases
Medicine & Health	PubMed/MEDLINE, Cochrane Library, CINAHL, Embase
Social Sciences	PsycINFO, Sociological Abstracts, ERIC
General/Multidisciplinary	Web of Science, Scopus, Google Scholar, JSTOR
Engineering & Technology	IEEE Xplore, ACM Digital Library
Humanities	JSTOR, Project MUSE, MLA International Bibliography

Step 3: Develop Your Search Strategy

• Identify keywords: Use synonyms and related terms (e.g., “adolescent,” “teenager,” “youth”)
• Use Boolean operators: AND narrows your search; OR broadens it; NOT excludes terms
• Apply truncation and wildcards: e.g., “therap*” captures therapy, therapies, therapist
• Use subject headings: Controlled vocabulary like MeSH terms (in PubMed) improves precision
• Set date filters: Limit to a relevant time period based on your topic’s history
• Document your search: Record exactly what you searched and when — this is essential for transparency and reproducibility

Step 4: Screen and Select Sources

Once you have your initial results, apply inclusion and exclusion criteria:

• Inclusion criteria might specify: peer-reviewed articles, published after a certain year, studies conducted in a specific population, written in a specific language
• Exclusion criteria might eliminate: conference abstracts, grey literature (unless doing a scoping review), studies below a quality threshold

For systematic reviews, screening should be done independently by at least two reviewers, with a clear process for resolving disagreements.

Step 5: Assess Source Quality

Not all published research is of equal quality. Ask yourself:

• Is it peer-reviewed?
• Is the methodology clearly described and appropriate?
• Is the sample size adequate?
• Are the conclusions supported by the data?
• Are there conflicts of interest?
• For qualitative studies: is the researcher’s positionality addressed?

Consider using validated appraisal tools such as the CASP checklists (Critical Appraisal Skills Programme) for different study designs.

Step 6: Supplement Your Search

• Backward searching: check the reference lists of key papers you have already identified
• Forward searching: use Google Scholar or Web of Science to find papers that have since cited a key article
• Grey literature: government reports, theses, and preprints may be relevant, particularly for scoping reviews

How to Synthesize the Literature

Synthesis is the intellectual core of a literature review. It is what distinguishes a literature review from an annotated bibliography.

Difference between Summary, Synthesis, and Evaluation of Literature

Activity	What It Means	Example
Summary	Recapping the key findings of a single source	“Smith (2020) found that exercise reduced anxiety scores by 30% in adults.”
Synthesis	Re-organising and connecting information across multiple sources to reveal relationships	“While Smith (2020) and Jones (2019) both found that exercise reduced anxiety, they differ on whether aerobic or resistance training is more effective.”
Evaluation	Assessing the worth, quality, or significance of a source	“However, Smith’s (2020) study is limited by its small, homogeneous sample, which may restrict generalizability.”

A strong literature review combines all three activities throughout.

Strategies for Effective Synthesis

• Group sources thematically rather than discussing one paper at a time. Cluster sources that address the same concept or finding
• Compare and contrast. Identify where researchers agree, disagree, or use conflicting methods
• Track developments over time. Note how thinking on a topic has evolved across decades
• Identify patterns. Look for recurring findings, dominant methodological approaches, or shared theoretical frameworks
• Highlight gaps: point out where has research been sparse, inconsistent, or entirely absent
• Build a synthesis matrix: a table with sources as rows and key themes or variables as columns helps you visualize connections and gaps before you start writing

Synthesis Matrix Example

Source	Population	Methodology	Key Finding	Limitations
Smith (2020)	Adults 18–40	RCT	Exercise ↓ anxiety by 30%	Small sample
Jones (2019)	Older adults	Cohort study	Resistance training most effective	No control group
Patel (2021)	Adolescents	Within-subjects design	Exercise improved self-efficacy	Self-report measures

What Synthesis Is NOT

• Stringing quotes together from different papers
• Summarizing each paper in a separate paragraph, one after the other
• Paraphrasing without analysis: true synthesis draws connections the original authors themselves may not have made explicit

As the San José State University Writing Center puts it, a literature review “synthesizes and evaluates the ideas of others on your given topic”. It is a conversation across sources, not a catalogue of them.

Literature Review for a Thesis or Dissertation: Special Considerations

A thesis or dissertation literature review carries unique expectations compared to a standalone review article.

Purpose Within the Thesis

The literature review in a thesis serves to:

• Establish the theoretical and conceptual framework you will work within
• Justify your research questions by showing what remains unknown or contested
• Demonstrate to examiners that you have a thorough, critical grasp of the field
• Provide the scholarly context that validates your chosen methodology
• Show original critical thinking  (not just coverage, but insight)

Key Differences from a Standalone Review

Feature	Thesis Literature Review	Standalone Review Article
Primary purpose	Grounds your original research	Is research in itself
Perspective	Written from your position as a researcher-in-progress	Addresses the broader scholarly community
Coverage	Selective but rigorous, must justify your study	May be exhaustive (systematic) or broadly representative (narrative)
Critical voice	Your analytical stance should be present throughout	Voice depends on review type
Evolution	May be revised as empirical work progresses	Fixed once published

Common Pitfalls for Thesis Writers

• Over-describing and under-analysing: spending too much time recounting what studies found and too little evaluating and connecting them
• Losing the thread: failing to link the discussion back to your own research question
• Neglecting seminal works: skipping foundational theories or landmark studies in your field
• No critical voice: presenting the literature as if all sources are equally valid and beyond debate
• Outdated coverage: not including recent publications. Always check for literature from the last 3–5 years before submission

How to Structure a Standalone Literature Review Article

A standalone literature review (published as a journal article) follows a recognizable structure. Review articles are among the most widely cited in academic literature, because they synthesize knowledge that others need as a starting point for their own research.

1. Title and Abstract

• The title should clearly signal the topic, scope, and review type (e.g., “A Systematic Review of…”; “Trends in… A Narrative Review”)
• The abstract should summarize the purpose, scope, methods (for systematic reviews), key findings, and conclusions

2. Introduction

The introduction should:

• Introduce the broader subject and establish its significance
• Narrow to your specific topic and the research question driving the review
• Define the scope: what time period, disciplines, and study types are included and why
• State the type of review being conducted
• Explain what the review contributes and how it is organized (a forecasting statement)

3. Methods (Required for Systematic, Scoping, and Descriptive Reviews)

For rigorous review types, a methods section must include:

• Search strategy: databases, date ranges, and search terms used
• Inclusion and exclusion criteria: clearly stated, ideally in a table
• Screening process: number of reviewers and how conflicts were resolved
• Quality appraisal: tools or criteria used to assess study quality
• Data extraction: what information was extracted and how
• A PRISMA flow diagram is standard for systematic reviews (Preferred Reporting Items for Systematic Reviews and Meta-Analyses)

4. Body / Results

Organize the body according to one of these approaches:

Organizational Approach	Description	Best For
Thematic	Groups sources by topic, concept, or finding	Most reviews; emphasizes intellectual connections
Chronological	Traces how knowledge has evolved over time	When historical development is important
Methodological	Groups by the methods used in primary studies	When comparing research approaches is the main goal
Theoretical	Groups by theoretical framework or school of thought	Theory-heavy disciplines like sociology or education

Within each section of the body:

• Provide background and definitions as needed
• Group and synthesize related findings. Do not move source by source
• Compare and contrast studies, and evaluate their methodological quality
• Note contradictions and debates
• Write topic sentences that express the analytical point of the paragraph, not just the name of a researcher

5. Discussion

Where present, the discussion:

• Draws together patterns and conclusions from across the body
• Addresses the implications of knowledge gaps for the field
• Evaluates the overall strength and consistency of the evidence base
• Suggests specific directions for future research

6. Conclusion

The conclusion should:

• Summarize the major contributions of the reviewed literature
• Reiterate what is known, what is contested, and what remains unknown
• Propose concrete avenues for future inquiry
• Avoid introducing new material not covered in the body

7. References

• Maintain a consistent citation style throughout (APA, MLA, Chicago, Vancouver, etc.)
• Cite both direct quotations and paraphrased material
• Use citation management software (Zotero, Mendeley, EndNote) to stay organized

Frequently Asked Questions

How many sources should a literature review include?

There is no universal rule. The appropriate number depends on the scope of your topic, the level of your work, and the type of review. A thesis chapter might include 40–80 sources; a short undergraduate paper might require 10–20; a comprehensive systematic review in medicine can include hundreds of primary studies. The key criterion is not quantity but coverage: have you engaged with the key theories, landmark studies, and recent developments relevant to your question? Check with your supervisor or your institution’s guidelines if you are unsure.

Can I include grey literature such as government reports, policy documents, or dissertations?

Yes, and in some cases you should. Grey literature can be valuable, particularly for scoping reviews or when the academic literature on a topic is sparse. Apply the same critical appraisal standards you would to any source: consider the authority of the producing organisation, the transparency of the methodology, and any potential for bias. Including grey literature is also important for systematic reviews because it helps reduce publication bias (the tendency for studies with positive or significant findings to be published more readily than those with null results).

How do I handle conflicting findings across sources?

Conflicting findings are a feature of the literature, not a problem to be hidden. They are often the most intellectually valuable thing a literature review can surface. Rather than ignoring contradictions, explore possible reasons for them: differences in study populations, methodologies, measurement tools, sample sizes, or time periods. Acknowledge where consensus is strong and where genuine debate exists. This kind of nuanced analysis signals to your reader that you understand the field deeply.

Should I include sources that contradict my thesis or position?

Absolutely. Engaging critically with contradictory evidence is a mark of scholarly integrity. Selectively citing only sources that support your position (sometimes called “cherry-picking”) is a serious academic flaw. A strong literature review acknowledges the full landscape of evidence, including studies that challenge your perspective, and explains why, on balance, the evidence or argumentation supports your position. As the University of Toronto advises, always ask yourself whether you have cited and discussed studies contrary to your own perspective.

When should I update my literature review?

Treat a literature review as a living document during the research process. For a thesis, update it whenever significant new publications appear, and always check for recent work before final submission. For published standalone reviews, the shelf life depends on the pace of the field: in fast-moving areas like biomedicine or artificial intelligence, reviews may become partially outdated within 2–3 years. As a general rule, if your database search was conducted more than 12–18 months ago in an active field, it is worth running updated searches before finalizing your manuscript.

References

1. Cantero, C. (2019). How to Write a Literature Review. San José State University Writing Center. https://www.sjsu.edu/writingcenter/docs/handouts/Literature%20Reviews.pdf
2. Alex, D. (2026). What is a Literature Review? How to Write It (with Examples). Paperpal Blog. https://paperpal.com/blog/academic-writing-guides/what-is-a-literature-review-how-to-write-it-with-examples
3. Paré, G., & Kitsiou, S. (2017). Chapter 9: Methods for Literature Reviews. In F. Lau & C. Kuziemsky (Eds.), Handbook of eHealth Evaluation: An Evidence-based Approach. University of Victoria. https://www.ncbi.nlm.nih.gov/books/NBK481583/
4. Taylor, D. (n.d.). The Literature Review: A Few Tips on Conducting It. Health Sciences Writing Centre, University of Toronto. https://advice.writing.utoronto.ca/types-of-writing/literature-review/
5. Institute for Academic Development, University of Edinburgh. (n.d.). Literature Review. https://institute-academic-development.ed.ac.uk/study-hub/learning-resources/literature-review

This article was originally published on April 3, 2024, and updated on June 3, 2026.