Grey literature is research that never enters commercial publishing: theses, university bulletins, technical reports, working papers, government publications, white papers, think-tank studies, conference proceedings. The content is scholarly. It just never appears in a publisher’s catalogue or a bookshop.
The name is usually explained like this. Material you can buy is white; material that is classified and stays inside is black; this sits in between. Not sold, not secret. Just hard to find.
The international definition
Charles P. Auger put the term into circulation in 1978, and the definition settled at a series of international conferences afterwards. The one adopted in Luxembourg in 1997 is still the most quoted:
Information produced on all levels of government, academia, business and industry in electronic and print formats not controlled by commercial publishing.
New York added a clause in 2004 — that publishing is not the primary business of the producing body — and the 2010 Prague definition brought in quality and intellectual property.
For practical purposes one point carries the rest: the organisation that produced it does not publish for a living. So there is no distribution machinery, no catalogue entry, and often no reason for a search engine to have indexed it.
What counts
| Type | Examples | Where it lives |
|---|---|---|
| Theses | Doctoral and master’s theses | Institutional repositories, national libraries |
| University and institute publications | Bulletins, annual reports, research reports | Institutional repositories |
| Technical reports | Technical reports, discussion papers | Institute websites, repositories |
| Government material | White papers, statistics, commissioned studies | Ministry websites, national libraries |
| Conference material | Proceedings, posters, slides | Society websites, repositories |
| Company and trade material | Company histories, trade-body reports | The issuing body, special libraries |
Whether preprints count is contested. They are certainly outside commercial publishing, but preprint servers are catalogued and searchable, so they lack the practical property that makes grey literature grey.
Why it is worth the extra searching
The results nobody submits are in here. Interventions that did not work and experiments that found no difference are less likely to reach a journal (publication bias). A report on the same topic often states the null result plainly. This is why systematic reviews search grey literature explicitly: to counterweight that bias.
Practitioner knowledge never goes to a journal in the first place. Municipal implementation reports, corporate technical reports, standards-body documents. Frequently the most detailed description of a method that exists, and never peer-reviewed anywhere.
Whole national literatures are largely grey. In Japan, for instance, university bulletins and theses are a thick layer of the scholarly record and are barely represented in international indexes. How you handle grey literature decides your coverage of that language entirely.
Where to look
Starting from a general search engine does not work well here. Go to the issuing body, or to whoever aggregates it.
Search institutional repositories across institutions. A repository is where a university or institute posts its own output. CORE and BASE aggregate them globally, as does OpenAIRE; in Japan the equivalent is IRDB, run by the National Institute of Informatics.
Use the national index for the language you need. For Japanese, CiNii Research covers articles, bulletins, theses and research data in one search. On 21 April 2026 its scope widened: alongside the papers, doctoral theses and research data it already took from IRDB, all remaining public IRDB content now arrives as “unclassified output”, so material types it used to miss now surface from the same box.
National library catalogues. NDL Search is the largest single window onto material published in Japan, theses and government publications included, and registered users can read digitised out-of-print material from home.
Go to the issuing body’s own site. If you already know the ministry,
institute or society, this is fastest. Their site search is usually poor, so
scope a web search with site: instead.
Field-specific collections. ERIC in education, RePEc in economics, clinical trial registries in medicine. Finding out whether your field has one is worth doing once.
Citing it
Grey literature does not arrive with clean bibliographic metadata. When you cite it, you assemble enough for a reader to reach the same document.
- Put the issuing organisation in the author position. There is often no named person.
- Always give the version and the date. Reports get replaced silently.
- URL and access date, or a DOI where one exists — repository deposits increasingly have them.
- Assume it will vanish. A site redesign takes reports with it. Save the PDF, and note an archived URL (Internet Archive, or the National Diet Library’s WARP) for anything load-bearing.
Most of it has not been peer reviewed, which is a reading instruction rather than a reason to avoid it: you are judging the strength of the evidence yourself.
Keeping what you find in one place
Searching grey literature means more windows: repositories, a national index, ministry sites, a field-specific collection. Results scattered across four tabs become results you cannot reconstruct three months later.
Litlas is built to collapse the collecting half. One search runs across 16 scholarly sources — including CORE and OpenAIRE Graph, which aggregate institutional repositories, arXiv for preprints, and OpenAlex, Crossref, DataCite and PubMed for everything else — and anything you keep goes into a library with your own notes and tags attached. PDFs you already have and records you type in yourself land in the same library, so grey literature and journal articles stay in one list rather than two. From any paper you can walk the citation graph backwards into what a report cites and forwards into who cited it.
Export is BibTeX, RIS or CSL-JSON, and references format in APA, Chicago (author-date), IEEE, MLA or Vancouver. The free plan needs no card and works right away.
Three things to remember
- Grey literature is not low-quality literature. It is literature with no distribution machinery, which changes only how you find it.
- Search repository aggregators (IRDB, CORE, BASE), the national index for the language, and the issuing body directly — not a general engine.
- Save it the moment you find it. A report URL does not last like a DOI.
Bibliography
- Auger, C. P. Use of Reports Literature. London: Butterworths, 1975.
- Ikeda, K. “Rethinking the Definition of Grey Literature” (in Japanese). Journal of Information Science and Technology, vol. 62, no. 2, 2012, pp. 50–54. https://doi.org/10.18919/jkg.62.2_50
- Ikeda, K. “Grey Literature in the Internet Era: Focusing on Change in the Definition of Grey Literature and the Pisa Declaration” (in Japanese). Journal of Information Processing and Management, vol. 58, no. 3, 2015, pp. 193–203. https://doi.org/10.1241/johokanri.58.193
- Ikeda, K. “Grey Literature Today: Trends of the 2010s” (in Japanese). Current Awareness, no. 340, 2019, CA1952. https://current.ndl.go.jp/ca1952
- National Diet Library. “NII Expands CiNii Research Coverage to All Public IRDB Content” (in Japanese). Current Awareness Portal, 22 April 2026. https://current.ndl.go.jp/car/277829
- Schöpfel, J. “Towards a Prague Definition of Grey Literature.” Twelfth International Conference on Grey Literature, Prague, 2010. https://shs.hal.science/sic_00581570v1