The Trust Territory of the Pacific Islands (TTPI) was a United Nations trust territory in Micronesia administered by the United States from 1947 to 1994. The Imperial Japanese South Seas Mandate had been seized by the US during the Pacific War, as Japan had administered the territory since the League of Nations gave Japan mandate over the area from Imperial Germany after World War I. However, in the 1930s, Japan left the League of Nations, and then invaded additional lands. During World War II, military control of the islands was disputed, but by the end of the war the islands had come under control of the Allies. The Trust Territory of the Pacific was created to administer the islands as part of the United States, while still under the auspices of the United Nations. Most of the island groups in the territory became independent states, with some degree of ties kept with the United States: the Federated States of Micronesia, Marshall Islands and Palau are today independent states in a Compact of Free Association with the US, while the Northern Mariana Islands remain under US jurisdiction, as an unincorporated territory and commonwealth.

The United Nations trust territories were the successors of the remaining League of Nations mandates, and came into being when the League of Nations ceased to exist in 1946. All the trust territories were administered through the United Nations Trusteeship Council and authorized to a single country. The concept is distinct from a territory temporarily and directly governed by the United Nations.