Edwin Thompson Denig entered the fur trade on the Upper Missouri River in 1833. As husband to the daughter of an Assiniboine headman and as a bookkeeper stationed at Fort Union, Denig became knowledgeable about the tribal groups of the Upper Missouri and was consulted by several noted investigators of Indian culture. When Denig was asked to respond to a circular by Schoolcraft, he didn’t simply rely on his own knowledge, but instead interviewed "in company with the Indians for an entire year" until he had obtained satisfactory answers.

Denig’s manuscript was unpublished until 1930, when J.N.B. Hewitt edited it for publication in the Smithsonian Bureau of American Ethnology’s Forty-sixth Annual Report. Long unavailable, this new edition provides a complete ethnology of the Assiniboine Indians, including information on their history, tribal organization and government, religion, manners and customs, warfare, dances, and language.