Idaho v. Coeur d'Alene Tribe of Idaho, 521 U.S. 261 (1997), was a United States Supreme Court case in which the Court held that the Coeur d'Alene Tribe could not maintain an action against the state of Idaho to press its claim to Lake Coeur d'Alene due to the state's Eleventh Amendment immunity from suit, notwithstanding the exception recognized in Ex parte Young. The case was an important precedent for aboriginal title in the United States and sovereign immunity in the United States.