The Supreme Court's main function is to determine the constitutionality of various laws, procedures and policies that come before it.
The Constitution specifies that the Supreme Court may exercise original jurisdiction in cases affecting ambassadors and other diplomats, and in cases in which a state is a party. In all other cases, however, the Supreme Court has only appellate jurisdiction. The Supreme Court considers cases based on its original jurisdiction very rarely; almost all cases are brought to the Supreme Court on appeal. In practice, the only original jurisdiction cases heard by the Court are disputes between two or more states.