United States is the country with the largest number of think tanks in the world, followed by China and India, according to a latest report of global think tanks rankings released by the Think Tanks and Civil Societies Program (TTCSP) at the University of Pennsylvania's International Relations Program.

This annual report named "The 2011 Global Go To Think Tank Rankings," the fifth edition of the kind, contains the most comprehensive rankings of the world's top think tanks, which has been described as the insider's guide to the global marketplace of ideas.

A total of 6,545 think tanks in the world were contacted and encouraged to participate in the nominations process, and a group of over 6000 scholars, journalists, policymakers, public and private donors, think tanks, and regional and subject area specialists were involved. The nominations and rankings were based on the detailed set of criteria, including the think tanks' production of rigorous and relevant research, publications, and programs in one or more substantive areas of research.

The following is the list of the top 25 countries and regions with the largest number of think tanks 2011: