A military is the most significant tool of a nation’s foreign policy, and (hopefully) the tool of last resort. Yet the control a civilian leader has over the military is, in many respects, an encumbered and fractured control. The military’s organizational culture, role in society, size, and considerable autonomy are potential obstacles to true civilian control over the military even in peacetime. A brief but historically informed text intended for students of the presidency or national security, addresses the gamut of challenges a new U.S. President faces as commander-in-chief.