North American Indian people of the Chiwere branch of the Siouan (Siouan languages) linguistic family, which also includes the closely related Missouri and Iowa tribes. In their historic past the Oto, together with the Iowa and the Missouri, separated from the Ho-Chunk and moved southwest. In 1673, when met by the Jacques Marquette (Marquette, Jacques) expedition, they were living some distance up the Des Moines River in present-day Iowa. By 1804 they were living near the mouth of the Platte River. In 1830 they ceded all their land in Missouri and Iowa to the United States government and ultimately sold off their remaining land in Kansas and Nebraska. In 1882 they were removed to Indian Territory (present-day Oklahoma).

Early 21st-century population estimates indicated some 2,500 individuals of Oto descent.