Grey literature is defined 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," according to GreyLit. They are often white papers, policies, proceedings or other documents that are outside the traditional publishing venues and, as such, may be difficult to find.
A lot of analysis published by think tanks or nonprofits is considered grey literature. Those organizations are quick to publish on specialized, highly relevant and sometimes very current topics and and have hired experts, practitioners and/or scholars, to do research and publish reports on the topic, contributing to grey literature*. Invariably, reports will be published from such organizations before scholarly articles can be written and published or government policy can be established. In fact, the mission (or agenda) of some of these organization is to inform and influence policy. In addition, in many cases, these think tanks are privately funded through donations or special interest groups. Therefore, it is critical to consider motivations behind the publication of reports from think tanks in addition to their methods.
Because there are so many think tanks, it is often difficult to distinguish between those that may have a more rigorous approach to researching issues. The Think Tanks and Civil Societies Program (TTCSP) at the Lauder Institute, University of Pennsylvania "conducts research on the role policy institutes play in governments and in civil societies around the world" and they publish a ranking of think tanks based on a survey of international scholars, grouped by issue area, regional focus and country of origin among others.
This search box will search the Public Policy Think Tanks listed below, many of which have been identified by the Global Go To Think Tank Report (from Penn):