This database is the largest policy directory which includes 24,000 organizations and 3 million publications.

Click on their Public Policy tab to find resources on 14 leading think tanks in the U.S.

The Brookings Institution is a nonprofit organization based in Washington, D.C. Their mission is to conduct in-depth, nonpartisan research to improve policy and governance at local, national, and global levels.

RAND is a research organization that develops solutions to public policy challenges to help make communities throughout the world safer and more secure, healthier and more prosperous.