Marbury v. Madison established that the Supreme Court has the final authority to declare laws unconstitutional. Chief Justice John Marshall ruled that when statutes conflict with the Constitution, courts must follow the Constitution and strike down the statute. This gave the judiciary power to check Congress and the President—a power the Constitution never explicitly grants but that Marshall argued flows from the Constitution's status as supreme law. This decision made the Court a co-equal branch of government and remains the foundation of American constitutional law.

Marbury v. Madison established that the Supreme Court has the final authority to declare laws unconstitutional. Chief Justice John Marshall ruled that when statutes conflict with the Constitution, courts must follow the Constitution and strike down the statute. This gave the judiciary power to check Congress and the President—a power the Constitution never explicitly grants but that Marshall argued flows from the Constitution's status as supreme law. This decision made the Court a co-equal branch of government and remains the foundation of American constitutional law.