Gray literature is a concept that refers to a wide variety of unpublished or informally published information from different groups such as professional associations, research institutes, government agencies, and non-profit organizations. It is usually difficult to track down this type of information because it is not published commercially (e.g. in a research journal), nor is it widely accessible.

For a more in-depth discussion of the definition of gray literature, please see "Toward a Prague Definition of Grey Literature" by Joachim Schoepfel, specifically page 18.

• Researchers
• Practitioners
• Policymakers
• Students

Gray literature comes in many different forms. Some examples include:

• Abstracts
• Reports
• Newsletters
• Preprints
• Journal supplements
• Working documents
• Theses & dissertations
• Clinical trials
• Bibliographies
• Book chapters
• Statistical documents
• White papers
• Conference proceedings
• Information communication (e.g. blogs, email, etc.)

Although it may be difficult to find, gray literature can be an important part of your research because it:

• Provides a very current perspective
• Fills in gaps present in the published literature
• Helps overcome a positive publication bias present in some of the published literature
• Compensates for a time-lag bias in the published literature
• May help provide a more international perspective

Like all information, gray literature has some potential weaknesses to be aware of:

• Lack of peer review
• Possibly less reliable / questionable quality
• Written for a purpose that may not be scientific (e.g. to promote a product)
• Potentially short information life cycle
• Document types can be very different, making it difficult to compare
• Searching may involve considerable time, effort and expense
• Access to full text or complete data may be a challenge
• Finding/indexing tools may not be readily available