The main objectives of this work are to examine the development of UN peace operations (and more specifically its transitional administrations) and also to verify how UNTAET worked in East Timor. The hypothesis to be analysed is that the weakness of institutions turned to governance generates a political context necessary (but not completely able) to explain the UN transitional administrations in the post-Cold War era. Particularly in East Timor, years of foreign domination and the occurrence of a war weakened severely the local institutions and in the UN view this could be a menace to the timorese independence process. In this case, UN chose to implement a transitional administration. However, it s necessary to observe that this concept is still under construction. Only after the end of the Cold War era and the beginning of the UN multidimensional peacekeeping operations, the theme of the transitional administrations gained more importance and particularly after the missions in Kosovo and East Timor, less than a decade ago.