"Umatilla Dictionary" documents the language of the Umatilla people east of the Cascade Mountains in Oregon and Washington. Working for many years with the accumulated scholarship of linguists and anthropologists as well as with elders on the Umatilla Reservation, tribal linguist Noel Rude has painstakingly recorded and rationalized words, pronunciations, phrases, and other elements of the Umatilla language.

The dictionary includes a grammar and comparative information that places the Umatilla language in its linguistic and historical context and compiles all of its known words, phrases, and constructions. "Umatilla Dictionary" is an important work for people of the Confederated Tribes of the Umatilla Indian Reservation, the Yakama Nation, and the Confederated Tribes of Warm Springs and adds to the growing linguistic work being done by tribes and scholars on endangered languages.