The Assiniboine, also known as the Assnipwan or sometimes the Stone Sioux, are a Native American people, originally from the Northern Great Plains area of North America, specifically in present-day Montana and parts of Canada around the US/Canadian border. This particular tribe was well known throughout much of the late 1700s and early 1800s. Images of tribal members were painted by such 19th century artists as Karl Bodmer and George Catlin. The tribe has many similarities to the Lakota (Sioux) people in lifestyle, linguistics, and cultural habits, and are considered to be a band of the "Nakoda" or middle division of the Lakota. It is believed that the Assiniboine broke away from other Lakota bands in the 17th century.

The Assiniboine were close allies and trading partners of the Cree, engaging in wars against the Atsina alongside them, and later fighting the Blackfoot. A Plains people, they generally went no further north than the North Saskatchewan River and purchased a great deal of European trade goods through Cree middlemen from the Hudson Bay Company.

The life style of this group was semi-nomadic, and they would follow the herds of bison during the warmer months. They did a considerable amount of trading with European traders, and worked with the Mandan, Hidatsa, and Arikara tribes, and that factor is strongly attached to their life style.

Though their description of the group was not all together favorable, the tribe's existence was noted in the journals of Lewis and Clark on their return journey from Fort Clatsop down the Missouri River. They had heard rumors that this was a ferocious group, and hoped to avoid contact with them. They did not see any sign of these people, and were not able to prove those rumors.