"Information produced on all levels of government, academics, business and industry in electronic and print formats not controlled by commercial publishing i.e. where publishing is not the primary activity of the producing body." (Luxembourg, 1997 - Expanded in New York, 2004, http://www.greynet.org/)
Grey literature may contain valuable information that cannot be found in academic journals.
Grey literature varies in terms of quality, and it is not always subject to a formal review process. As with any information source, it is important to review it carefully.
The following collections of resources offer suggested search engines or databases that can be used to look for different types of grey literature: