Grey literature is information produced outside of traditional publishing and distribution channels, and can include reports, policy literature, working papers, newsletters, government documents, speeches, white papers, urban plans, and so on.
This information is often produced by organizations "on the ground" (such as government and inter-governmental agencies, non-governmental organizations, and industry) to store information and report on activities, either for their own use or wider sharing and distribution, and without the delays and restrictions of commercial and academic publishing. For that reason, grey literature can be more current than literature in scholarly journals.
However, because grey literature (usually) does not go through a peer review process, the quality can vary a great deal. Be sure to critically evaluate your source.
For an extensive list of the types of documents that might be considered grey literature, see Document types in grey literature (from GreyNet International).
To search across the websites of governments and organizations, use the resources below.
Another way to find grey literature is to identify organizations that might be publishing this type of information on topics that you're interested in and then to search their websites — paying close attention to website sections with names like "Documents", "Reports", and "Library". Consider government agencies, non-profits, professional associations, research institutes, and other organizations, based on the research you have already done.
Use Google's site limits to only search a government or institution's site or top-level domain, for instance use site:.gov to limit your search to US government sites. Use site:.org to limit your search to organizations. This technique paired with keywords in Google is a quick way to locate grey literature. Example search: site:.gov universal free meals
Type your search terms into these pre-built searches to limit results to specific organization types.
NGO Search
NGO Search is a Google Custom Search that searches across hundreds non-governmental organization (NGO) websites. NGO Search is a project of the International Documents Taskforce (IDTF) and the Government Documents Roundtable (GODORT) of the American Library Association (ALA). This is a spreadsheet of NGOs included in the project.
IGO Search
International governmental organizations (IGOs) are organizations made up of more than one national government—examples include NATO (North Atlantic Treaty Organization) and the WHO (World Heath Organization). The governments are the members. IGO Search is a Google Custom Search that searches across IGO websites. It is a project of the International Documents Taskforce (IDTF) and the Government Documents Roundtable (GODORT) of the American Library Association (ALA). Here is the growing spreadsheet of IGO urls included in the search.