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Grey literature (or gray literature) is a library and information science term that refers to informally published written material (such as reports) that may be difficult to trace via conventional channels such as published journals and monographs because it is not published commercially or is not widely accessible. It may nonetheless be an important source of information for researchers, because it tends to be original and recent. Examples of grey literature include patents, technical reports from government agencies or scientific research groups, working papers from research groups or committees, white papers, and preprints.
The identification and acquisition of grey literature poses difficulties for librarians and other information professionals for several reasons. 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. In 1995, D.B. Simpson observed that "peripheral materials, including grey literature, expand unabated. Libraries having difficulty collecting traditional materials have little hope of acquiring the periphery".
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 as falling under the heading of grey literature, although they again share some of the same problems of control and access. 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 free on the World Wide Web. The impact of this trend has been greatly boosted since the early 2000s by the growth of major search engines such as Google, Yahoo! and Bing. Grey reports are thus far more easily found online than they were, and at radically lower cost, at least in the immediate aftermath of their publication. 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 document online reports or publications adequately (often omitting a publication date, for instance); because documents are rarely assigned permanent URLs or DOI numbers, or stored in electronic depositories, so that broken links can develop; and because the copyright status of many reports is left unclear, inhibiting their downloading and electronic storage. Securing long-run or secure access to grey literature in a predominantly digital age thus remains a considerable problem, as does archiving or overviewing such materials.
The concept of grey literature has 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 recognised 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 widely accepted, by, among others, the Grey Literature Network Service. It emphasises the supply side of grey literature, namely its production and publication both in print and electronic formats. It calls attention to the question of dissemination, and the difficulty of identifying and accessing documents described as ephemeral, non-conventional or underground.
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". This definition accords with Mackenzie Owen’s 1997 observation that "grey does not imply any qualification [but] is merely a characterization of the distribution mode".
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.
Towards a New Definition 
The 12th International Conference on Grey Literature at Prague in December 2010 discussed a new approach to grey literature. It concluded that the existing definition of grey literature—the New York definition—remained helpful and should not be replaced, but that it needed to be adapted to the changing environment. The definition was insufficient in the context of Internet publishing, and that further attributes were needed to differentiate grey from other items.
The proposal was to add four attributes to the New York definition:
- The document character of grey literature (concept of the French multidisciplinary network)
- Legal nature of works of the mind, e.g., protection by intellectual property.
- A minimum quality level (peer review, label, validation).
- The link to intermediation, e.g., the interest of grey items for collection (and not for the end user).
The proposal for a new definition ("Prague Definition") of grey literature is as follows:
"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 intermediation. Without the revision mentioned above, the current definition risks becoming obsolete due to its inability to differentiate grey literature from other documents.
The proposal for a revised “Prague definition” brings together the former economic approach with new attributes. The next step should be to check this definition against common usage in libraries and different types of grey and other documents. Once done, the value of the definition can be evaluated on the basis of the answers to the following two questions: does this new definition include all kind of documents usually considered by LIS professionals as grey literature, including today’s difficult-to-process and hard-to-collect items, and does it lead to further differentiation or better understanding of how grey literature may be distinguished from other forms of literature? Three challenges in particular are said to face professionals in the field at the present moment:
- The development of institutional repositories by publishing organizations as a complementary and sometimes concurrent service to tradition library holdings; and the place and processing of grey literature in theses archives.
- The tendency of disintermediation in the traditional value chain of scientific and technical information. The “risk” of grey literature is not web-based technology but the somehow fading role of libraries and information professionals as intermediaries between authors, publishing bodies, and the end user. And tell the reader why this is important other than job preservation.
- The so-called "Fourth Paradigm", e.g., data-intensive science and the access to datasets that together generate a trend to transform and/or marginalise literature.
Typology of grey literature 
The term traditionally referred to reports, conference proceedings and doctoral theses. In the OpenSIGLE repository, reports are the most numerous among the different types of grey literature. The "reports" category covers a wide variety of very different documents: institutional reports, annual or activity reports, project or study reports, technical reports, reports published by ministries, laboratories or research teams, etc. Some are disseminated by national and international public bodies; others are confidential, protected, or disseminated to a restricted readership, such as technical reports from industrial R&D laboratories. Some are voluminous, with statistical appendices, while others are only a few pages in length.
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, personal communications, working papers, house journals, laboratory research books, preprints, academic courseware, lecture notes, and so on. The international network GreyNet maintains an online listing of document types.
Malin-grey literature 
"Malin-grey literature" refers to publications whose construction and self-referencing are actively construed to avoid the attention of information professionals. Typically such professionals employ various parameters in identifying which publications are suited to incorporation within a particular collection. To avoid dissemination and archiving the authors of malin-grey literature employ the absence of bibliographical indicators, deception, disinformation, rapid decomposition (or other self-destructive construction), obscurity or atypical formats. Malin-grey literature differs from samizdat, or underground literature, in that samizdat publications only seek to disguise the identities of the author and distributor, whereas malin-grey literature seeks actively to prevent or obstruct dissemination.
Some commentators have suggested that the name derives from the French for "deceptive ingenuity"; others, less convincingly, claim that it is a reference to Anne-Marie Malingrey (fl. 1960s-70s), a French historian.
Grey literature has a role of its own as a means of distributing scientific and technical 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.
A Franco-Dutch study reviews 64 citation analyses published between 1987 and 2005, citing altogether several thousand references. The table below shows the proportion of grey literature cited in publications from different scientific disciplines.
|Field||Grey literature citations in %|
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 conventional distribution media (journals), while in others, such as agriculture, aeronautics and the engineering sciences in general, grey literature resources tend to predominate.
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.
According to another study, grey literature seems also to play a considerable part in the library and information sciences, accounting on average around 20% of all sources used a figure that may be compared with the citation habits in economics and educational sciences. Even so, citations to grey material vary widely between different papers from 0% to 50% and more, depending on subject areas and methodologies.
Grey Literature International Steering Committee 
The Grey Literature International Steering Committee (GLISC) was established in 2006 after the 7th International Conference on Grey Literature (GL7) held in Nancy (France) on 5–6 December 2005.
During this conference, the Istituto Superiore di Sanità (ISS) (Rome, Italy) presented guidelines for the production of scientific and technical reports included in the wider category of grey literature. The Italian initiative for the adoption of uniform requirements for the production of reports was discussed during a Round Table on Quality Assessment by a small group of GL producers, librarians and information professionals who agreed to collaborate in the revision of the guidelines proposed by ISS. The group approving these guidelines—informally known as the “Nancy Group”—has been formally defined as the Grey Literature International Steering Committee (GLISC).
The Guidelines include ethical principles related to the process of evaluating, improving, and making reports available and the relationships between GL producers and authors. The latter sections address the more technical aspects of preparing and submitting reports. GLISC believes the entire document is relevant to the concerns of both authors and GL producers.
GreyNet Resources 
Since 1993, GreyNet International, the Grey Literature Network Service, organizes the International Conferences Series on Grey Literature, producing a substantial body of scientific and professional papers on grey literature:
- 1993 GL1 Amsterdam, “GL’93, Weinberg Report 2000” 
- 1995 GL2 Washington D.C. ”GL’95, Grey Exploitations in the 21st Century” 
- 1997 GL3 Luxembourg, “GL’97, Perspectives on the Design and Transfer of STI” 
- 1999 GL4 Washington D.C., “GL’99, New Frontiers in Grey Literature” 
- 2003 GL5 Amsterdam, “Grey Matters in the World of Networked Information” 
- 2004 GL6 New York, “Work on Grey in Progress” 
- 2005 GL7 Nancy, France “Open Access to Grey Resources”
- 2006 GL8 New Orleans, “Harnessing the Power of Grey”
- 2007 GL9 Antwerp, “Grey Foundations in Information Landscape”
- 2008 GL10 Amsterdam, “Designing the Grey Grid for Information Society”
- 2009 GL11 Washington D.C., “The Grey Mosaic: Piecing It All Together”
- 2010 GL12 Prague (CZ), “Transparency in Grey Literature: Grey Tech Approaches to High Tech Issues”
- 2011 GL13 Washington D.C., "The Grey Circuit : From Social Networking to Wealth Creation", Library of Congress 5–6 December 2011, http://www.opengrey.eu/search/request?q=publisher%3A%28Amsterdam+%3A+TextRelease%2C+2012%29
- 2012 GL14 Rome, "Tracking Innovation through Grey Literature" National Research Council 29–30 November 2012
- 2013 GL15 Bratislava, "The Grey Audit, A Field Assessment of Grey Literature" CVTISR, 2-3 December 2013 (Forthcoming)http://www.textrelease.com/gl15callforpapers.html
Currently, the conference papers from GL1 to GL13 are openly available in the OpenGrey Repository, http://www.opengrey.eu
GreyNet also organizes GreyWorks the Summer Workshop Series on Grey Literature:
- GreyWorks 2009, Amsterdam, "Benchmarks and Forecasts on Grey Literature"
- GreyWorks 2010, Washington D.C., "Transparency Governs the Grey Landscape"
- GreyWorks 2011, Amsterdam, "Ten Strategies for Grey Literature"
- GreyWorks 2012, The Hague, "Strategic Mapping of Grey Literature"
GreyNet likewise publishes the only international scientific journal on grey literature, The Grey Journal (ISSN print 1574-1796, ISSN e-print 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 the Scopus database and other A&I services.
The Grey Journal, International Journal on Grey Literature:
- TGJ Volume 9, Number 1, Spring 2013 Adapting New Technologies for Grey Literature
- TGJ Volume 8, Number 1, Spring 2012 Social Networking and Grey Literature
- TGJ Volume 8, Number 2, Summer 2012 Data Frontiers in Grey Literature
- TGJ Volume 8, Number 3, Autumn 2012 Managing Change in Grey Literature
- TGJ Volume 7, Number 1, Spring 2011 Transparency in Grey Literature
- TGJ Volume 7, Number 2, Summer 2011 System Approaches to Grey Literature
- TGJ Volume 7, Number 3, Autumn 2011 Research and Education in Grey Literature
- TGJ Volume 6, Number 1, Spring 2010 Government Alliance to Grey Literature
- TGJ Volume 6, Number 2, Summer 2010 Shared Strategies for Grey Literature
- TGJ Volume 6, Number 3, Autumn 2010 Research on Grey Literature in Europe
- TGJ Volume 5, Number 1, Spring 2009 Paperless Initiatives for Grey Literature
- TGJ Volume 5, Number 2, Summer 2009 Archaeology and Grey Literature
- TGJ Volume 5, Number 3, Autumn 2009 Trusted Grey Sources and Resources
- TGJ Volume 4, Number 1, Spring 2008 Praxis and Theory in Grey Literature
- TGJ Volume 4, Number 2, Summer 2008 Access to Grey in a Web Environment
- TGJ Volume 4, Number 3, Autumn 2008 Making Grey more Visible
- TGJ Volume 3, Number 1, Spring 2007 Grey Standards in Transition and Use
- TGJ Volume 3, Number 2, Summer 2007 Academic and Scholarly Grey
- TGJ Volume 3, Number 3, Autumn 2007 Mapping Grey Resources
- TGJ Volume 2, Number 1, Spring 2006 Grey Matters for OAI
- TGJ Volume 2, Number 2, Summer 2006 Collections on a Grey Scale
- TGJ Volume 2, Number 3, Autumn 2006 Using Grey to Sustain Innovation
- TGJ Volume 1, Number 1, Spring 2005 Publish Grey or Perish
- TGJ Volume 1, Number 2, Summer 2005 Repositories - Home2Grey
- TGJ Volume 1, Number 3, Autumn 2005 Grey Areas in Education
GreyNet International Business Report 2013:
What the Furture holds in Store for GreyNet International, http://greynet.org/home/aboutgreynet.html
In the ongoing discussion on new business models of academic publishing, eScience and open access to public research results, non-commercial distribution channels will continue to play a central role as vectors of scientific communication, alongside commercial publishing.
Another question is about impact and usage. In the past, impact metrics were limited to citations and journals. Today, usage metrics offer new opportunities to measure impact of a large scale of digital resources, also on the individual item level. Tomorrow, these metrics will provide additional information on quality and popularity to the end user.
Open archives will offer more appropriate services and functions for at least some segments of grey literature if not for all. But bibliographic control of grey literature will remain problematic despite the trend toward standardization of digital documents. And the libraries, together with their scientific communities, need to find new forms for the fundamental functions of scientific publishing, applied to open repositories, non-commercial items and datasets.
See also 
- European Association for Grey Literature Exploitation: EAGLE
- System for Information on Grey Literature in Europe: SIGLE
- Grey Literature Network Service: GreyNet
- Grey Literature International Steering Committee: GLISC
- Debachere, M.C. (1995). "Problems in obtaining grey literature". IFLA Journal 21 (2): 94–98. doi:10.1177/034003529502100205.
- Auger, C.P., ed. (1989). Information Sources in Grey Literature (2nd ed.). London: Bowker-Saur. ISBN 0862918715.
- Simpson, D.B. (1996). "Grey Literature: the challenges for an increasingly important body of research literature". Grey exploitations in the 21st century: 2nd International conference on grey literature. ISBN 9074854087.
- Auger, C.P., ed. (1975). Use of Reports Literature. London: Butterworth. ISBN 040870666X.
- 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.
- Owen, J. Mackenzie (1997). "Expanding the Horizon of Grey Literature". Third International Conference on Grey Literature: Perspectives on the Design and Transfer of Scientific and Technical Information. Amsterdam: Transatlantic D F. ISBN 9074854176.
- Farace, D.J.; Schöpfel, J., eds. (2010). Grey Literature in Library and Information Studies. Berlin: De Gruyter Saur. ISBN 9783598117930.
- T. Hey, et al. (eds.) (2009). The Fourth Paradigm. Data-Intensive Scientific Discovery. Microsoft Corporation.
- D. Farace, et al. (2005). `Acces to Grey Content: An Analysis of Grey Literature based on Citation and Survey Data: A Follow-up Study'. In GL7 Conference Proceedings. Seventh International Conference on Grey Literature: Open Access to Grey Resources .
- Infocult: Malin-grey, what are you?
- Copac: Anne-Marie Mailngrey
- Malingrey A M
- Sondergaard T. F.; Andersen J.; Hjorland B. Documents and the communication of scientific and scholarly information. Revising and updating the UNISIST model. Journal of Documentation 2003, 59, (3), 278-320.
- Abel R. Book and Journal Publishing. In Encyclopedia of Library and Information Science. May 14, 2004, 1-9.
- J. Schöpfel, et al. (2005). `Citation Analysis and Grey Literature: Stakeholders in the Grey Circuit'. vol. 1, pp. 31-40.
- Ullah M.F.; Kanwar S.S.; Kumar P. A quantitative analysis of citations of research reports published by National Institute of Hydrology, Rorkee. Annals of Library and Information Studies 2004, 51, (3), 108-115.
- J. Schöpfel & D. J. Farace (2010). `Grey Literature'. In M. J. Bates & M. N. Maack (eds.), Encyclopedia of Library and Information Sciences, Third Edition, pp. 2029-2039. CRC Press, London.
Further reading 
- Braun, Janice and Lola Raykovic Hopkins. “Collection-Level Cataloging, Indexing, and Preservation of the Hoover Institution Pamphlet Collection on Revolutionary Change in Twentieth Century Europe”. Technical Services Quarterly 12:4 (1995): 1-8.
- Childress, Eric and Erik Jul. "Going Gray: Gray Literature and Metadata". Journal of Internet Cataloging 6:3 (2003): 3-6.
- Denda, Kayo. “Fugitive Literature in the Cross Hairs: An Examination of Bibliographic Control and Access”. Collection Management 27:2 (2002): 75-86.
- D. J. Farace & J. Schöpfel (eds.) (2010). Grey Literature in Library and Information Studies. De Gruyter Saur.
- Harrison, John. 2005.Grey Literature or Fugitive Report Project . MLA Forum, 4(1).
- Hirtle, Peter. 1991. Broadsides vs. Gray Literature. Available: http://www-cpa.stanford.edu/byform/mailing-lists/exlibris/1991/1 I/msgOO02O.htm (June 15, 1997).
- Information World. 1996. What is gray literature? Available: http://info.learned.co.uk/li/newswire/I196/wiII96.htm, (June 18, 1997).
- P. Pejsova (ed.) (2010). Grey Literature Repositories. Radim Bacuvcik VeRBuM, Zlin CZ.
- Schöpfel, Joachim. Observations on the Future of Grey Literature. The Grey Journal 2:2 (2006): 67-76. Available:  (December 2009)
- J. Schöpfel & D. J. Farace (2010). `Grey Literature'. In M. J. Bates & M. N. Maack (eds.), Encyclopedia of Library and Information Sciences, Third Edition, pp. 2029-2039. CRC Press.
- Seeman, Corey. "Collecting and Managing Popular Culture Material: Minor League Team Publications as "Fringe" Material at the National Baseball Hall of Fame Library". Collection Management 27:2 (2002): 3-20.
- 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, p. 510-515.
- White, Herbert. 1984. Managing the Special Library. White Plains, N. Y.: Knowledge Industries Publications, Inc.
- About grey literature in medical systematic reviews
- ALA Internet Resources: Gray Literature
- GreyNet: The Grey Literature Network Service
- 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
-  CiteSeerX indexes some of the gray literature such as technical reports in computer and information science
-  OpenGrey Repository, formerly OpenSIGLE