Think tanks are "policy advice institutions"; and vary in their approaches. They provide research and current analysis, advocate for policy change, and promote the views of individuals or parties.
Source: Hartwig Pautz, Think Tanks, Social Democracy and Social Policy (New York: Palgrave Macmillan, 2012), accessed October 15, 2012, http://www.palgraveconnect.com/doifinder/10.1057/9780230368545