The Arapaho (in French: Arapahos, Gens de Vache) are a tribe of Native Americans historically living on the eastern plains of Colorado and Wyoming. They were close allies of the Cheyenne tribe and loosely aligned with the Sioux. Arapaho is an Algonquian language closely related to Gros Ventre, whose people are seen as an early offshoot of the Arapaho. Blackfoot and Cheyenne are the other Algonquian-speakers on the Plains, but their languages are quite different from Arapaho. By the 1850s, Arapaho bands had coalesced into two tribes: the Northern Arapaho and Southern Arapaho.
Since 1878 the Northern Arapaho Nation has lived with the Eastern Shoshone on the Wind River Reservation in Wyoming. This is the seventh-largest reservation in the United States. The Southern Arapaho Tribe live with the Southern Cheyenne in Oklahoma. Together their members are enrolled as a federally recognized tribe, the Cheyenne and Arapaho Tribes.