Book excerpt: With the range of security challenges confronting the United States in the 21st century, characterized by competition by both state and nonstate actors, the importance of working with allies and partners to address common challenges is paramount. Deeper examination of the relative effectiveness of U.S. security sector assistance and how it must nest in a broader foreign policy strategy, including good governance, human rights, and rule of law principles, is required. Improving oversight and accountability in U.S. security sector assistance with partners are at the core of ongoing security assistance reform efforts to ensure that U.S. foreign policy objectives are met and in accordance with U.S. interests and values. This report examines key areas in security sector programming and oversight where the U.S. Departments of Defense and State employ accountability mechanisms, with the goal of identifying ways to sharpen and knit together mechanisms for improving accountability and professionalism into a coherent approach for partner countries.