Indian law deals with the relationships among Indians, tribes, and federal and state governments. Can a state impose a sales tax on a reservation smoke shop and its customers? Can a state require an Indian to have a state fishing license? Who will prosecute crimes committed by non-Indians on Indian reservations? And on and on.
Sources of law include treaties between the United States and tribes, federal statutes, and federal cases. (There are state statutes and state cases, as well.)