The main types of academic sources are journal articles, books and chapters, preprints, theses and dissertations, reports and other grey literature, datasets, conference papers and reference works such as encyclopedias. Each is a different kind of evidence: a research article reports a study, a review sums up many, a preprint has not been peer reviewed, and an encyclopedia entry is background you read rather than cite.
EdCitation publishes this guide, drawn from the library guides of eight universities, two preprint servers, APA Style and Wikipedia's page on academic use, read on 26 and 27 September 2026. The date beside each library guide is the one its page gave as last updated.
EdCitation does three of the jobs below at no cost and without sign-up. The Source type filter in Find sources limits a search to one kind of work; Cite a source turns a DOI or ISBN into a reference taken from the record; Verify references looks up every entry of a finished list to show it exists.
What are the types of academic sources?
The table gives each type, what the guides say it is for, and where to find it. Your own brief always wins: an instructor can rule a type in or out.
| Source type | What it is | When to use it | How to find it | Source |
|---|---|---|---|---|
| Research article | A journal article reporting the authors' own study | Evidence for a claim | A subject database, or Article in the Source type filter of Find sources | UC Merced Library (2026a) |
| Review article | A journal article that compares many studies | Mapping a field; finding its key studies | Review article in Find sources | UC Merced Library (2026a) |
| Book or chapter | An edited overview, usually by experts | Background, theory, classic arguments | The library catalogue; Book, Book chapter | University of Exeter Library (2026) |
| Preprint | A paper posted before, or without, peer review | New work; cite the journal version once it exists | arXiv, Preprints.org; Preprint | arXiv (n.d.); Preprints.org (n.d.) |
| Thesis or dissertation | The document submitted for a degree | Detailed data, long bibliographies; check your brief | Repositories, ProQuest; Dissertation or thesis | Davidson College Library (2026) |
| Report and grey literature | Work published outside commercial publishing | Policy, statistics, practice | Government and organisation sites; Report | Oregon State University Libraries (2026a) |
| Dataset | Structured data, often with its own DOI | Your own analysis; where figures came from | Data repositories; Dataset | University of Michigan Library (2026) |
| Conference paper | A paper given at a conference, often published after | New work, in computing especially | Proceedings databases; In conference proceedings | University of Exeter Library (2026) |
| Reference work | Encyclopedias, dictionaries, handbooks | Background and definitions; rarely cited | Reference collections; Encyclopedia or reference entry | Mount Royal University Library (2026) |
Primary, secondary and tertiary sources: what is the difference?
A primary source is first-hand evidence, a secondary source analyses or interprets primary sources, and a tertiary source collects or indexes the other two. That is how UC Merced Library (2026b) defines them: primary sources made at or near the time by witnesses or recorders, secondary sources that interpret an event or phenomenon, tertiary sources used to locate the rest.
What counts as primary depends on the subject. Virginia Commonwealth University Libraries (2026) says so, and adds that, depending on the research question, any source, even a tertiary one, can serve as a primary source.
In the sciences
The primary source is the article that first reports an experiment or trial. UC Merced Library (2026b) lists the results of experiments, research and clinical trials as the sciences' primary sources, and its guide to article types calls review articles secondary, because their authors synthesise others' findings instead of reporting their own (UC Merced Library, 2026a).
In the humanities and social sciences
Here primary sources are the objects of study: creative works, diaries, interviews, news footage and maps in the humanities; census data, statistics and experiments on human behaviour in the social sciences (UC Merced Library, 2026b). VCU's worked example runs one topic through all three: for a question about Wonder Woman, a 1977 comic is primary, a video interview about the character's origins secondary, and a book compiling that history tertiary.
Where the guides disagree
Theses are the awkward case. The University of Exeter Library (2026) lists dissertations among its secondary sources, yet on the same page says theses hold substantial primary research. Both hold: a thesis's own study is primary, its literature review secondary. If a brief asks for "primary sources", ask what the person who set it means in that subject.
Journal articles: research article or review article?
A research article reports one study its authors carried out; a review article compares the results of many. UC Merced Library (2026a) warns that the two can share the same headings, so the test is whether the authors present findings of their own.
Use a recent review to learn the field's vocabulary and find its key studies, then read and cite those studies for the claims they support. A review's account of a study is a paraphrase, and the risk of citing what you have not read is set out in I cited a source I did not read. Narrative, systematic and scoping reviews are compared in types of literature review.
Is a preprint a reliable source?
A preprint is less reliable than the published version of the same paper, because it has not been peer reviewed, and the servers themselves are plain about it. arXiv (n.d.) calls itself a curated platform whose material "is not peer-reviewed by arXiv"; moderation checks only that a submission is on topic and of scholarly value. Preprints.org (n.d.) states that its content is not peer reviewed, describes a screening of under a day for basic scientific content, author background and ethics, and asks readers to reuse preprints with caution.
When a preprint is acceptable
APA Style prefers the final published version; a preprint is cited only when it is the version you actually read (American Psychological Association, 2020a). In fast fields a preprint may be all there is: the University of Oxford Bodleian Libraries (2026) computer science guide lists arXiv as a free resource, with arXiv's own warning attached.
So look for a journal version first. Preprints.org says it links one from the preprint's page when it appears; the preprint cited below, Bhardwaj and Sharma (2021), had none in its Crossref record on 27 September 2026. Checking whether any article went through review is covered in our peer review guide.
Can I cite a thesis or dissertation?
Yes, usually, but check your brief first. Davidson College Library (2026) notes that dissertations are not always peer reviewed like journal articles and that some professors rule them out, while pointing out that they often hold new research and long bibliographies that lead to peer-reviewed work.
Oregon State University Libraries (2026b) files theses under grey literature and lists where to search them, including university repositories, ProQuest Dissertation Express, PQDT Open, Open Access Theses and Dissertations and the Networked Digital Library of Theses and Dissertations. If the research was later published as an article, cite the article. In APA, the degree and the awarding institution go in square brackets, then the repository (American Psychological Association, 2020b); see how to cite a dissertation or thesis.
Reports, grey literature, datasets and conference papers
These are the types a database search misses most often.
Grey literature examples
Grey literature is government, academic and business work shared outside traditional publishing, and it is usually not peer reviewed. Oregon State University Libraries (2026a) lists working papers, government and NGO publications, technical reports, conference proceedings, slides, newsletters, dissertations, blog posts and talks, and asks of each: who made it, what are their biases, and are they respected in the field?
One example: the World Health Organization (2019) technical report Microplastics in drinking-water, with an ISBN, on WHO's own site. For a public health essay it is what a marker expects; for one laboratory result, cite the study it draws on. Company and market reports are covered in citing sources in a business report.
Datasets
A dataset is cited with its author, title, year, archive, version and a persistent identifier. The University of Michigan Library (2026) says citing data credits its producer and helps others find it, and that a DOI should replace a URL where one exists.
Conference papers
The University of Exeter Library (2026) describes conference papers as often the first public presentation of research, warns that some are never published, and notes that many are peer reviewed. In computing, where the Bodleian's guide puts proceedings beside journals, a refereed conference paper is often cited as it stands; elsewhere, look for a journal article that followed.
Can I cite an encyclopedia or Wikipedia?
Usually not: read it for background, then cite the sources it leads to. Mount Royal University Library (2026) calls Wikipedia and similar sites fine for getting started but usually not acceptable to cite, since they are not peer reviewed and change quickly. Wikipedia's own page on academic use agrees, and advises citing the original sources an article names (Wikipedia, 2026). A signed entry in a specialist subject encyclopedia is a different case that some briefs allow.
How do I cite each type of source?
EdCitation's Cite a source builds each type's reference from a DOI, ISBN, title or web address in APA 7, MLA 9, Chicago 18 author-date, Harvard, IEEE and Vancouver. The patterns are in our guides to a book or ebook, a textbook chapter, a dissertation or thesis and a website in APA 7, and style by style at APA, MLA, Chicago, Harvard, IEEE and Vancouver.
How do I search by source type in Find sources?
For a brief that names the kinds of source it wants, EdCitation's Find sources is the strongest first stop, because its Source type filter narrows about 300 million published works to one kind before you read anything. The panel offers twelve boxes: Article, Review article, Book chapter, Book, Preprint, Dissertation or thesis, Report, Dataset, Editorial, Letter, Encyclopedia or reference entry, Standard. Conference papers sit under Where it was published, as In conference proceedings. Every result is looked up in the record; nothing is written for you.
The runs, 27 September 2026
The test search was microplastics in drinking water. Every run was answered by the back-up index, which serves results while the main index is busy and names any filter it could not apply.
- No type ticked: 1,804,373 results. The first page held 98: 70 articles, 19 preprints, 6 book chapters, 2 dissertations, 1 conference paper. First: a 2025 systematic review in the journal Microplastics, cited 34 times.
- Preprint: 57,279 results; all 90 on the first page preprints. First: "Pathways of Microplastics from Urban Water Systems to Drinking Water and Human Exposure", posted in 2026 with an SSRN DOI. No notice, so the filter applied.
- Dissertation or thesis: 5,625 results; all 100 theses. First: a 2026 PhD thesis from Vrije Universiteit Amsterdam on measuring microplastics in freshwater, drinking water and fish. The third, a 2008 thesis on Jakarta's water service, never mentions microplastics in its title: read before keeping.
- Review article: the response listed it under unsupported, and the results page prints "The full index is busy, so these filters are not applied right now: Review article." The 1,442,503 results mixed reviews and studies, because the back-up index files a review as a journal article. On such a run, add review to the search words.
- Book gave 3,863 results and Dataset 4,829, with no notice; In conference proceedings gave 96,663, all 99 on the first page conference papers.
Types follow how each publisher registered its record: an Oxford chapter came back under Book, and an AccessScience encyclopedia entry and a clinical trial registration under Dataset. Check the type on the source's own page.
Citing a journal article, a preprint and a book
Cite a source built these APA 7 entries. From the DOI 10.3389/fchem.2018.00407:
Mason, S. A., Welch, V. G., & Neratko, J. (2018). Synthetic polymer contamination in bottled water. Frontiers in Chemistry, 6, Article 407. https://doi.org/10.3389/fchem.2018.00407
The title is in sentence case, as APA asks for article titles. From the preprint DOI 10.20944/preprints202104.0498.v1:
Bhardwaj, L. K., & Sharma, A. (2021). Microplastics (MPs) in drinking water: Uses, sources & transport. Preprints.org. https://doi.org/10.20944/preprints202104.0498.v1
It names the server, Preprints.org, as APA asks, though the record files the subject "EARTH SCIENCES" where a server's name often goes. The title is in sentence case, with the initialism MPs kept. From the ISBN 9780226239736:
Booth, W. C., Colomb, G. G., Williams, J. M., Bizup, J., & FitzGerald, W. T. (2016). The craft of research (4th ed.). University of Chicago Press.
No change needed, and no retraction was reported for any of the three. Two other runs: the thesis DOI 10.5463/thesis.1638 gave "[Doctoral dissertation, Vrije Universiteit Amsterdam]", the awarding university APA asks for, not the repository that deposited it; and the WHO report's ISBN, 9789241516198, came back "No book is recorded under ISBN 9789241516198." Reports are often missing from book catalogues, so cite one from its web address.
Checking a mixed list with Verify references
We pasted five corrected entries of five types into Verify references, with one planted slip: The craft of research given as the 3rd edition.
- Journal article, preprint and thesis: verified, "The DOI resolves to this record and the title matches."
- WHO report: verified, "The page is at this address, and its title matches."
- Booth: "check this", "The publisher's record for 2016 is the 4th edition, not the 3rd. Check the edition and year."
Verified means the work exists as described, not that a preprint or thesis suits your assignment; that is the brief's call.
What is free and what is paid
Find sources, Cite a source and Verify references cost nothing and need no sign-up. Pro, $8 a month, adds References from a file: upload the paper, and each reference is checked and each citation in the text tied to its list entry. The Max plan, $24 a month, brings the Library of textbooks and scholarly books. Nothing in a student's paper is written by EdCitation; it finds, cites and checks sources, and the argument stays yours. The full search method is set out in how to find sources for a literature review fast.
Quick questions
Is a preprint a reliable source?
Less reliable than a published article, because it has not been peer reviewed; arXiv and Preprints.org both say so. Cite the journal version if there is one.
Can I cite a thesis in my essay?
Usually, unless your brief rules theses out, as some instructors do. If the research was later published as an article, cite that.
What are some grey literature examples?
Government and NGO reports, working papers, technical reports, conference proceedings, theses, newsletters and slides. Most are not peer reviewed.
Is a textbook a primary or secondary source?
Secondary, or tertiary when it mainly compiles other work. The University of Exeter Library lists textbooks among secondary sources.
Can EdCitation search for one type of source only?
Yes. Tick a box under Source type in EdCitation's free Find sources to limit results to articles, preprints, theses, books, datasets or seven other types; a type the index could not apply on a run is named on the page.
References
- American Psychological Association. (2020a). Preprint article references. APA Style. https://apastyle.apa.org/style-grammar-guidelines/references/examples/preprint-article-references
- American Psychological Association. (2020b). Published dissertation or thesis references. APA Style. https://apastyle.apa.org/style-grammar-guidelines/references/examples/published-dissertation-references
- arXiv. (n.d.). About arXiv. https://info.arxiv.org/about/index.html
- Bhardwaj, L. K., & Sharma, A. (2021). Microplastics (MPs) in drinking water: Uses, sources & transport. Preprints.org. https://doi.org/10.20944/preprints202104.0498.v1
- Booth, W. C., Colomb, G. G., Williams, J. M., Bizup, J., & FitzGerald, W. T. (2016). The craft of research (4th ed.). University of Chicago Press. https://doi.org/10.7208/chicago/9780226239873.001.0001
- Davidson College Library. (2026, April 13). All about dissertations. https://davidson.libguides.com/c.php?g=1082118&p=8232745
- Mason, S. A., Welch, V. G., & Neratko, J. (2018). Synthetic polymer contamination in bottled water. Frontiers in Chemistry, 6, Article 407. https://doi.org/10.3389/fchem.2018.00407
- Mount Royal University Library. (2026, September 14). How can I use Wikipedia (or sources like it) for my assignments? https://libraryhelp.mtroyal.ca/faq/211258
- Oregon State University Libraries. (2026a, September 16). Gray literature: Beyond peer review. https://guides.library.oregonstate.edu/c.php?g=1118911
- Oregon State University Libraries. (2026b, September 16). Theses & dissertations. https://guides.library.oregonstate.edu/c.php?g=1118911&p=8160163
- Preprints.org. (n.d.). About. https://www.preprints.org/about
- UC Merced Library. (2026a, May 1). Empirical articles vs review articles. https://libguides.ucmerced.edu/identifying-locating-empirical-articles/comparing-articles
- UC Merced Library. (2026b, June 16). Primary, secondary and tertiary sources. https://libguides.ucmerced.edu/source-types
- University of Exeter Library. (2026, September 7). Identify information types. https://libguides.exeter.ac.uk/c.php?g=668304&p=4742048
- University of Michigan Library. (2026, September 25). Citing data & statistics. https://guides.lib.umich.edu/c.php?g=282964&p=3285995
- University of Oxford Bodleian Libraries. (2026, September 22). Journals and conference proceedings: Computer science. https://libguides.bodleian.ox.ac.uk/computer_science/journals-and-conference
- Virginia Commonwealth University Libraries. (2026, April 13). Identify primary, secondary, tertiary sources. https://guides.library.vcu.edu/sources
- Wikipedia. (2026, May 19). Wikipedia:Academic use. https://en.wikipedia.org/wiki/Wikipedia:Academic_use
- World Health Organization. (2019). Microplastics in drinking-water. https://www.who.int/publications/i/item/9789241516198