There is no single definition of who is considered an Indian. To be eligible for some federal benefits, one must be a member of a federally recognized tribe, have at least half Indian ancestry, or be 1/4 or more Indian with ancestry from the US. Native Americans have been US citizens since 1924. Reservations are lands reserved by tribes when they relinquished other areas to the US, with the largest being the Navajo Reservation. Tribes have their own governments and laws apply differently on and off reservations. The federal government recognizes tribal sovereignty but also oversees relationships between tribes and the federal government.