Given the scope of authority the United Nations has assumed in order to perform functions of territorial administration both in East Timor and Kosovo, it is, as one commentator remarked, rather surprising that the issue of the legitimacy of the internationalisation of state structures through post-conflict governance has inspired little debate. There are myriad reasons for the erosion of political authority in a territory temporarily administered by the international community – corruption, local obstructionism and internal divisions, failure to promote government transparency, a tenuous link between civil administration and the military command structure, the operation of (inter)national networks of patronage, and general incompetence, to name a few. This article analyses some of the inherent tensions involved in international institution-building. It introduces the variety of actors operating in an internationalised territory as the quest for legitimacy creates tensions between them, and portrays the dynamics that unfold in a process in which notions of legitimacy are subject to institutional contestation.