The United Nations Transitional Administration in East Timor (UNTAET) was established by the UN Security Council on 25 October 1999 to administer the territory of East Timor towards independence in the wake of its violent separation from Indonesia. UNTAET largely fulfilled the elements of the security and governance mandate conferred on it by the Security Council, but this was not sufficient to create the conditions for lasting stability in the territory in the absence of a positive internal political settlement. In the process of constructing the machinery for the new state, UNTAET influenced the character of the political settlement that was taking shape across Timor's elites and the wider society in unintended ways. To demonstrate this, this article considers three areas: the political space that opened up under UNTAET; the organization of the transitional government; and constitution-making for the future state of Timor-Leste. The article concludes that UNTAET misread the local context, leading it to pay insufficient attention to the complex political dynamic playing out around it and to the profound institutional consequences of its policy choices.