Establishes criminal justice responsibilities among American Indian tribes with tribal land, the states in which tribes are located, and the federal government. Public Law 280 is mandatory or optional for 204 tribes, about two-thirds of the total in the lower 48 states. In states where P.L. 280 does not apply, the federal government retains criminal jurisdiction for major crimes committed under the Indian Country Crimes Act (18 U.S.C. § 1152), the Indian Country Major Crimes Act (18 U.S.C. § 1153), and the Assimilative Crimes Act (18 U.S.C. § 13).