Congress’s recent focus on reducing federal spending raises questions about the relative efficiency and effectiveness of all federal programs. In this context, evaluation of foreign assistance programs is of growing interest to many Members of Congress as they scrutinize the Administration’s international affairs budget request and debate foreign aid spending priorities. Policymakers, taxpayers, and aid recipients alike want to know what impact, if any, foreign aid dollars are having, and whether foreign aid programs are achieving their intended objectives. In most cases, the success or failure of U.S. foreign aid programs is not entirely clear, in part because historically, most aid programs have not been evaluated for the purpose of determining their actual impact. The purpose and methodologies of foreign aid evaluation have varied over the decades, responding to political and fiscal circumstances. Aid evaluation practices and policies have variously focused on meeting program management needs, building institutional learning, accounting for resources, informing policymakers, and building local oversight and project design capacity. Challenges to meaningful aid evaluation have varied as well, but several are recurring.