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Grey Literature

What is grey literature?

Grey literature refers to information that is not published through traditional commercial or academic publishing channels. It encompasses a broad range of material and is not well represented in indexing sources. 

Established definitions of grey literature 

"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. when publishing is not the primary activity of producing body" (Schöpfel, 2010, p. 1).

Grey literature is diverse and comes in a variety of forms, it is composed of knowledge artefacts that are not the product of peer-review processes or is not published in a traditional format. This can include (re)sources unlikely to be systematically collected such as conference proceedings, dissertations and theses, raw data, or reports generated by Institutional Repositories, or Government agencies (Adams et al., 2017).

Grey Literature Tutorial

Watch the short video below from Western University describing what grey literature is and how it can help in the research process. 


Grey literature is used for many reasons which will differ to your field of research. Some of the key reasons is that it:

  •   Introduces alternate viewpoints
  •   Is the only source of information - e.g. research data, letters and unpublished studies
  •   Provides first hand accounts of events - e.g. research data, diaries
  •   Overcomes or minimises reporting or publication biases; grey literature is more likely to include negative results - e.g. clinical trials
  •   Provides new information not yet published in traditional sources - e.g. conference papers
  •   Provides more local information - e.g. government reports, local collections
  •   Is a source of raw data such as data sets and statistics (James Cook University Library, 2023)


Apart from sometimes being irretrievable, other considerations about grey literature are that it:

  • Is often excluded from large databases and other mainstream sources
  • Is not peer-reviewed
  • Can often be difficult to locate (you can consider using an internet archive such as The WayBack Machine)
  • May only be available in obsolete formats
  • May not be publicly available and will need to be requested from organisations/government bodies
  • Is part of the Invisible web

It is important to note that, while not considered scholarly, grey literature is often produced by experts in a field. Searchers will need to use evaluative methods to assess the accuracy and validity of the literature collected. 

What should I include?

There are several types of grey literature, each with its unique characteristics and purpose. To some extent, the type of grey literature you need depends on your question and the evidence required to answer it. 

You should carefully consider the types of grey literature you will and will not include in your review. The word cloud below summarises some common types of grey literature.

These sections of the Cochrane Handbook recommend specific types of grey literature to be searched for compliant systematic reviews.

Word cloud image generated using 



Adams, R. J., Smart, P., & Huff, A. S. (2017). Shades of grey: Guidelines for working with the grey literature in systematic reviews for management and organizational studies. International Journal of Management Reviews: IJMR, 19(4), 432–454.
Schöpfel, J. (2010, December 6-7). Towards a Prague Definition of Grey Literature. [Conference preprint]. Twelfth International Conference on Grey Literature: Transparency in Grey Literature. Grey Tech Approaches to High Tech Issues. Prague, Czech Republic.