Bolstering local perceptions of legitimacy in armed intervention has emerged as an important feature of increasingly complex international peace and statebuilding efforts. Yet, previous research has only begun to explore what local legitimacy entails to those involved in, and affected by, armed intervention. This dissertation advances an understanding of local legitimacy as a perception-based, relational phenomenon. Through this lens, it examines armed intervention in Afghanistan (2001-2014). In particular, this dissertation studies how the relationship between Afghan citizens and intervening armed forces interacts with, and shapes, perspectives on local legitimacy held by the main 'interveners' and those 'intervened upon'. This dissertation consists of an introduction, which situates the study in a wider context, and four essays. Beginning with the organizational perspectives of the main intervening actors in Afghanistan, Essay I finds that the UN and NATO initially conceptualized problems of local legitimacy as principally the consequence of a fragile Afghan state, and not as failings of the intervention. When negative dimensions of intervention became increasingly recognized, principal responsibility for the legitimacy process shifted away from intervening authorities and onto the Afghan state. Similarly, Essay II shows how key U.S. military doctrine, over time, reconceptualized the formal duty of intervening forces in the local legitimacy process, ultimately considering it contingent on, and subordinate to, the will and capabilities of host-state authorities and the local population. Turning thereafter to firsthand accounts from the field, Essay III and Essay IV together contrast personal perspectives on the intervention held by U.S. Army Officers and Afghan citizens. Essay III finds that personal experiences of noncombat contact with Afghans reinforced the Officers' sense of duty toward the local population. Conversely, Essay IV suggests that the local legitimacy of intervening forces became increasingly contested among Afghans, due largely to the perceived intensification of foreign intrusion on 'everyday' life. Taken together, the findings of this dissertation lay the foundation for the development of a new concept, the host-citizen contract. In so doing, it provides a social contract framework to better understand the complex dynamics of local legitimacy in Afghanistan, and beyond.