The Department of State and the Department of Defense (DOD) have long shared responsibility for U.S. assistance to train, equip, and otherwise engage with foreign military and other security forces. The legal framework for such assistance emerged soon after World War II, when Congress charged the Secretary of State with responsibility for overseeing and providing general direction for military and other security assistance programs and the Secretary of Defense with responsibility for administering such programs. Over the years, congressional directives and executive actions have modified, shaped, and refined State Department and DOD roles and responsibilities. Changes in the legal framework through which security assistance to foreign forces—weapons, training, lethal and nonlethal military assistance, and military education and training—is provided have responded to a wide array of factors. This book provides an overview of U.S. assistance to and engagement with foreign military and other security forces, focusing on Department of State and DOD roles. It lays out the historical evolution and current framework of the Department of State-DOD shared responsibility.