The Confederated Tribes of the Umatilla Indian Reservation (CTUIR) is a union of three tribes: Cayuse, Umatilla, and Walla Walla. The CTUIR has more than 3,000 tribal members, almost half of whom reside on the reservation's 172,000 acres. The CTUIR is governed by a constitution and by-laws adopted in 1949. The governing body, the Board of Trustees, is supported by a staff of more than 500 employees working in natural resources, health, public safety, education, social services, public works, economic development and other areas.

In 1855, the three tribes signed a treaty with the US government in which it ceded over 6.4 million acres to the US. In the treaty, the tribes reserved rights to fish, hunt, and gather foods and medicines within ceded lands, which today is northeastern Oregon and southeastern Washington. Tribal members still exercise and protect those rights today.

The CTUIR owns and operates many successful enterprises, providing jobs for tribal members and communities. Wildhorse Resort & Casino employs about 1,100 and Cayuse Holdings, about 700. Other enterprises are Arrowhead Travel Plaza, Mission Market, Tamástslikt Cultural Institute, Indian Lake Campground, Coyote Business Park, and Nixyaawii Community Financial Services, to name a few.

The CTUIR publishes a monthly newspaper, the Confederated Umatilla Journal, which has received numerous awards, and supports a its own public radio station, KCUW 104.3 FM.