Grey literature (or gray literature) is a type of information or research output produced by organisations, outside of commercial or academic publishing and distribution channels. Grey literature may be in print or digital form and common grey literature publication types include reports (annual, research, technical, project etc.), working papers, government documents, and evaluations. Organisations that produce grey literature include government departments and agencies, civil society or non-governmental organisations, academic centres and departments, and private companies and consultants.
Grey literature may be made available to the public, or distributed privately within an organisation or group, and often lacks systematic means of distribution and collection. The standard of quality, review and production can also vary considerably. Grey literature is therefore often difficult to discover, access and evaluate.
The concept of grey literature has gradually emerged since the 1970s. When Charles P. Auger published the first edition of his landmark work on "reports literature" in 1975, he did not use the term "grey literature". Nevertheless, his account of this "vast body of documents", with its "continuing increasing quantity", the "difficulty it presents to the librarian", its ambiguity between temporary character and durability, and its growing impact on scientific research, was entirely compatible with what is now called grey literature. While acknowledging the challenges of reports literature, he also recognized that it held a "number of advantages over other means of dissemination, including greater speed, greater flexibility and the opportunity to go into considerable detail if necessary". For Auger, reports were a "half-published" communication medium with a "complex interrelationship [to] scientific journals". Only in the second edition of his book, published in 1989, did he adopt the term "grey literature".
The so-called "Luxembourg definition", discussed and approved at the Third International Conference on Grey Literature in 1997, defined grey literature as "that which is produced on all levels of government, academics, business and industry in print and electronic formats, but which is not controlled by commercial publishers". In 2004, at the Sixth Conference in New York, a postscript was added for purposes of clarification: grey literature is "...not controlled by commercial publishers, i.e., where publishing is not the primary activity of the producing body". This definition has since been used extensively and is widely accepted.
The U.S. Interagency Gray Literature Working Group (IGLWG), in its "Gray Information Functional Plan" of 1995, defined grey literature as "foreign or domestic open source material that usually is available through specialized channels and may not enter normal channels or systems of publication, distribution, bibliographic control, or acquisition by booksellers or subscription agents".
Other terms used for this material, both in the past and still today, include report literature, government publications, policy documents, fugitive literature, nonconventional literature, unpublished literature, non-traditional publications and many others. With the introduction of desktop publishing and the internet, new terms added to the list include electronic publications, online publications, online resources, open access research, digital documents, etc.
While the term grey literature is fairly obscure and difficult to define, it has the advantage of being an agreed collective term that researchers and information professionals and researchers can use to group and discuss this distinct group of resources.
In 2010 D.J. Farace and J. Schöpfel pointed out that existing definitions of grey literature were predominantly economic, and argued that in a changing research environment, and with new channels of scientific communication, grey literature needed a new conceptual framework. They proposed a new definition ("Prague Definition"): "Grey literature stands for manifold document types produced on all levels of government, academics, business and industry in print and electronic formats that are protected by intellectual property rights, of sufficient quality to be collected and preserved by library holdings or institutional repositories, but not controlled by commercial publishers i.e., where publishing is not the primary activity of the producing body."
Today, due to the overwhelming success of web publishing and access to documents focus has shifted to quality, intellectual property, and curation. Without the revision mentioned above, the current definition risks becoming obsolete due to its inability to differentiate grey literature from other documents.
Production and publication types
The term grey literature refers to a large number of resource types including institutional reports, annual or activity reports, project or study reports, technical reports, government reports, research reports etc. In the other categories, citation analyses offer a wide range of grey resources. Besides theses and conference proceedings, they also include unpublished manuscripts, newsletters, recommendations and technical standards, patents, technical notes, product catalogs, data and statistics, presentations, malin-grey literature, working papers, field notes, laboratory research books, preprints, academic courseware, lecture notes, and so on. The international network GreyNet maintains an online listing of document types.
Organisations produce grey literature as a means of encapsulating, storing and sharing information, for their own use and for wider distribution. This can take the form of a record of data and information on a site or project (archaeological records, survey data, working papers); sharing information on how and why things occurred (technical reports and specifications, briefings, evaluations, project reports); describing and advocating for changes to public policy, practice or legislation (white papers, discussion papers, submissions); meeting statutory or other requirements for information sharing or management (annual reports, consultation documents); and many other reasons.
Organisations are often looking to create the required output and share it with relevant parties quickly and easily, without the delays and restrictions of academic journals or book publishing. There is often little incentive or justification for organisations or individual staff members to publish in academic journals or books, and often no need to charge for access to organisational outputs. Indeed, some information organisations may be required to make public. On the other hand grey literature is not necessarily always free, with market reports in particular, selling for thousands of dollars. This is however the exception, and on the whole though, grey literature, while costly to produce, is usually made available for free.
While the production and research quality may be extremely high (with the reputation of the organisation vested in the end product), the producing body, not being a formal publisher, generally lacks the channels for extensive distribution and bibliographic control.
Information and research professionals generally draw a distinction between ephemera and grey literature. However, there are certain overlaps between the two media and they undoubtedly share common frustrations such as bibliographic control issues. Unique written documents such as manuscripts and archives, and personal communications, are not usually considered to fall under the heading of grey literature, although they again share some of the same problems of control and access.
The relative importance of grey literature is largely dependent on research disciplines and subjects, on methodological approaches, and on sources used. In some fields, especially the life sciences and medical sciences, there has been a traditional preference for only using peer-reviewed academic journals while in others, such as agriculture, aeronautics and the engineering sciences in general, grey literature resources tend to predominate.
In the last few decades, systematic literature reviews in health and medicine have established the importance of discovering and analysising grey literature as part of the evidence-base and to avoid publication bias.
Grey literature is particularly important as a means of distributing scientific and technical and public policy and practice information. Professionals insist on its importance for two main reasons: research results are often more detailed in reports, doctoral theses and conference proceedings than in journals, and they are distributed in these forms up to 12 or even 18 months before being published elsewhere. Some results simply are not published anywhere else.
In particular, public administrations and public and industrial research laboratories produce a great deal of “grey” material, often for internal and in some cases “restricted” dissemination. The notion of evidence-based policy has also seen some recognition of the importance of grey literature as part of the evidence-base however the term is not yet widely used in public policy and the social sciences more broadly.
For a number of reasons, discovery, access, evaluation and curation of grey literature pose a number of difficulties.
Generally, grey literature lacks strict bibliographic control, meaning that basic information such as author, publication date or publishing body may not be easily discerned. Similarly, the nonprofessional layouts and formats, low print runs, and non-conventional channels of distribution of grey literature make the organized collection of such publications challenging compared to journals and books.
Although grey literature is often discussed with reference to scientific research, it is by no means restricted to a single field: outside the hard sciences, it presents significant problems in, for example, archaeology, in which site surveys and excavation reports, containing unique data, have frequently been produced and circulated in informal "grey" formats.
Many of the problems of accessing grey literature have decreased since the late 1990s as government, professional, business and university bodies have increasingly published their reports and other official or review documents online. The impact of this trend has been greatly boosted since the early 2000s by the growth of major search engines. Grey reports are thus far more easily found online than they were, often at no cost to access. Most users of reports and other grey documents have migrated to using online copies, and efforts by libraries to collect hard-copy versions have generally declined in consequence.
However, many problems remain because originators often fail to produce online reports or publications to an adequate bibliographic standard (often omitting a publication date, for instance). Documents are often not assigned permanent URLs or DOI numbers, or stored in electronic depositories, so that link rot can develop within citations, reference lists, databases and websites. Copyright law and the copyrighted status of many reports inhibits their downloading and electronic storage and there is a lack of large scale collecting of digital grey literature. Securing long-term access to and management of grey literature in the digital era thus remains a considerable problem.
The amount of digital grey literature now available also poses a problem for finding relevant resources and to be able to assess their credibility and quality given the number of resources now available. At the same time a grey deal of grey literature remains hidden either not made public or not discoverable via search engines.
Grey literature databases
Various databases and libraries collect and make available some level of grey literature.
Many university libraries provide subject guides that give information on databases.
Grey literature resources and advocacy
The annual International grey literature conference series has been organised since 1993 by the Europe-based organisation GreyNet Research in this field of information has been systematically documented and archived via the International Conference Series on Grey Literature (1993, Vol.1)...(2014, Vol.16)
Greynet also produces a journal on grey literature and has been a key advocate for the recognition and study of grey literature, particularly in library and information sciences. The Grey Journal (2005, Vol.1)...(2014, Vol.10). (print: ISSN 1574-1796, online: ISSN 1574-180X). The Grey Journal appears three times a year—in spring, summer, and autumn. Each issue in a volume is thematic and deals with one or more related topics in the field of grey literature. The Grey Journal appears both in print and electronic formats. The electronic version on article level is available via EBSCO's LISTA-FT Database (EBSCO Publishing). The Grey Journal is indexed by Scopus and others.
On 16 May 2014, the Pisa Declaration on Policy Development for Grey Literature Resources was ratified and published.
- European Association for Grey Literature Exploitation
- System for Information on Grey Literature in Europe
- Auger, C.P., ed. (1975). Use of Reports Literature. London: Butterworth. ISBN 040870666X.
- Auger, C.P., ed. (1989). Information Sources in Grey Literature (2nd ed.). London: Bowker-Saur. ISBN 0862918715.
- Schöpfel, J.; Farace, D.J. (2010). "Grey Literature". In Bates, M.J.; Maack, M.N. Encyclopedia of Library and Information Sciences (3rd ed.). Boca Raton, Fla.: CRC Press. pp. 2029–2039. ISBN 9780849397127.
- Farace, D.J.; Schöpfel, J., eds. (2010). Grey Literature in Library and Information Studies. Berlin: De Gruyter Saur. ISBN 9783598117930.
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- Schöpfel, Joachim. Observations on the Future of Grey Literature. The Grey Journal 2:2 (2006): 67–76. Available:  (December 2009)
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- Sulouff, P., et al. Learning about gray literature by interviewing subject librarians: A study at the University of Rochester. College & Research Libraries News, 66(7) 2005, pp. 510–515.
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- About grey literature in medical systematic reviews
- ALA Internet Resources: Gray Literature
- GreyNet: The Grey Literature Network Service
- Grey literature strategies research project
- Science.gov is a gateway to over 50 million pages of authoritative selected science information provided by U.S. government agencies, including research and development results.
- http://www.scienceaccelerator.gov/ Science Accelerator searches science, including R&D results, project descriptions, accomplishments, and more, via resources made available by the Office of Scientific and Technical Information (OSTI), U.S. Department of Energy
- The GrayLIT network: A science portal of technical reports. From the Office of Scientific & Technical Information at the United States Department of Energy.
- Grey Literature Library for UK Archaeology
- The International Journal on Grey Literature published one volume in 2000. The content may be limited to subscribers.
- CiteSeerX indexes some of the gray literature such as technical reports in computer and information science
- OpenGrey Repository, formerly OpenSIGLE
- Pisa Declaration on Policy Development for Grey Literature Resources