The Confederated Tribes of the Umatilla Indian Reservation are the federally recognized confederations of three Sahaptin-speaking Native American tribes who traditionally inhabited the Columbia River Plateau region: the Cayuse, Umatilla, and Walla Walla.

When the leaders of the Walla Walla, Cayuse, and Umatilla peoples signed the Treaty of Walla Walla with the United States in 1855, they ceded 6.4 million acres (26,000 km2) of their homeland that is now northeastern Oregon and southeastern Washington. This was done in exchange for a reservation of 250,000 acres (1,000 km2) and the promise of annuities in the form of goods and supplies.

The tribes share the Reservation, which consists of 271 square miles (700 km2) in Umatilla County, in northeast Oregon state. The tribes have created a joint political structure as part of their confederation. The tribal offices are just east of Pendleton, Oregon. Almost half of the reservation land is owned by non-Native Americans; the reservation includes significant portions of the Umatilla River watershed. In 2013 the three-tribe confederation populated about 2,916 people, roughly half of the tribal population live on or near the reservation.The reservation is also home to about 300 Native Americans enrolled with other Tribes, such as the Yakama, Tenino (Warm Springs), and Nez Percé. 1,500 people who are not Native American also reside within the reservation boundaries.