This brief provides a detailed analysis of a first-of-its-kind, publicly available repository of U.S. think tank funding — www.thinktankfundingtracker.org. The repository tracks funding from foreign governments, the U.S. government, and Pentagon contractors to the top 50 think tanks in the United States over the past five years. It serves as a vital research guide for anyone wishing to learn more about the funding sources of prominent U.S. think tanks.