Marbury v. Madison, 5 U.S. (1 Cranch) 137 (1803), was a landmark decision of the U.S. Supreme Court that established the principle of judicial review, meaning that American courts have the power to strike down laws and statutes they find to violate the Constitution of the United States. Decided in 1803, Marbury is regarded as the single most important decision in American constitutional law. It established that the U.S. Constitution is actual law, not just a statement of political principles and ideals. It also helped define the boundary between the constitutionally separate executive and judicial branches of the federal government.
The case originated in early 1801 and stemmed from the rivalry between outgoing President John Adams and incoming President Thomas Jefferson.