This chapter explores the concept of military duty in the context of contemporary war. It focuses on the recent developments in the normative and strategic frameworks of Western military operations, which emphasize that mission effectiveness is largely dependent on the security and wellbeing of the local population. This has seemingly stretched the traditional notion of military duty, which is to master and apply organized military force to achieve political objectives and defeat the enemy on the battlefield. Based on empirical insights from the U.S. military and its recent missions in Iraq and Afghanistan, the chapter argues that this development has created tensions between political and military understandings of duty, as well as between organizational and individual notions of duty within the U.S. military. Conflicting notions of military duty hold important policy implications to both domestic civil-military relations and U.S. military power abroad because they challenge the integrity of political objectives and threaten military cohesion and unity of effort with regard to the management of local populations during war.