SourceWatch - Think tanks Good description of what a think tank - or policy institute is and does followed by a list of Examples links to think tanks
List of Think Tanks in the United States Wikipedia alphabetical list of links to think tank web sites. See also and international List of think tanks
Worldpress.org’s index of international think tanks and research organizations
Think Tanks & Foreign Policy Program ranks the influence and effectiveness of policy institutes in an annual document: The Global "Go-To Think Tanks”: The Leading Public Policy Research Organizations in the World, 2016 pdf
Life in the Tank: What really happens inside all those think tanks? Slate.com By Katy Waldman, Wednesday, March 7, 2012