The Mission was established on 25 October 1999 by the adoption of the Security Council Resolution 1272.
 
The main goals of the Mission are to provide security and maintain law and order throughout the territory of East Timor, to establish an effective administration, to assist in the development of civil and social service and to support capacity-building for self-government.
 
UNMISET / UNAMET / UNTAET medal was established on 9 December 1999. The ribbon has two outer bands of UN blue, representing the UN presence in East Timor. Inside the two bands, there are two equal bars - closest to the blue, the bar is crimson, with the bar closest to the center being sunrise yellow. These colours represent the brilliant and spectacular sunrises and sunsets experienced in East Timor. The center of the ribbon is a band of white, traditionally the colour of peace and hope, the goal this Mission seeks to achieve. Qualifying time of service for the reception of UNMISET / UNAMET / UNTAET medal is 90 days.