An American Indian reservation is an area of land held and governed by a U.S. federal government-recognized Native American tribal nation, whose government is autonomous, subject to regulations passed by the United States Congress and administered by the United States Bureau of Indian Affairs, and not to the U.S. state government in which it is located. Some of the country's 574 federally recognized tribes govern more than one of the 326 Indian reservations in the United States, while some share reservations, and others have no reservation at all. Historical piecemeal land allocations under the Dawes Act facilitated sales to non–Native Americans, resulting in some reservations becoming severely fragmented, with pieces of tribal and privately held land being treated as separate enclaves. This jumble of private and public real estate creates significant administrative, political, and legal difficulties.

The Dawes Act of 1887 regulated land rights on tribal territories within the United States. Named after Senator Henry L. Dawes of Massachusetts, it authorized the President of the United States to subdivide Native American tribal communal landholdings into allotments for Native American heads of families and individuals. This would convert traditional systems of land tenure into a government-imposed system of private property by forcing Native Americans to "assume a capitalist and proprietary relationship with property" that did not previously exist in their cultures. The act allowed tribes the option to sell the lands that remained after allotment to the federal government. Before private property could be dispensed, the government had to determine which Indians were eligible for allotments, which propelled an official search for a federal definition of "Indian-ness".