The Osage Nation (/ˈs/ OH-sayj) (Osage: ?? ??????͘ (Ni-u-kon-ska), "People of the Middle Waters") is a Midwestern Native American tribe of the Great Plains. The tribe developed in the Ohio and Mississippi river valleys around 700 BC along with other groups of its language family. They migrated west after the 17th century, settling near the confluence of the Missouri and Mississippi rivers, as a result of Iroquois invading the Ohio Valley in a search for new hunting grounds.

The term "Osage" is a French version of the tribe's name, which can be roughly translated as "calm water". The Osage people refer to themselves in their indigenous Dhegihan Siouan language as ?????? (Wazhazhe), or "Mid-waters".

By the early 19th century, the Osage had become the dominant power in the region, feared by neighboring tribes. The tribe controlled the area between the Missouri and Red rivers, the Ozarks to the east and the foothills of the Wichita Mountains to the south. They depended on nomadic buffalo hunting and agriculture.