Especially useful are the 3 major portals to the output of think tanks, NGOs and policy research organisations: Overton Policy Documents; Harvard Think Tank Search; Policy Commons
For some major general sources of open access e-books and e-journals please see the Library's Open Access Content page. Other open access resources are distributed across this guide depending upon their geographical or topical focus
Grey literature is information not produced by commercial publishers. It includes research reports, working papers, conference proceedings, theses, preprints, white papers, and reports produced by government departments, academics, business and industry. It can be hard to track down, but the resources listed below are good starting points, and see also the links to think tank/NGO policy reports here.