Marbury v. Madison, 5 U.S. (1 Cranch) 137 (1803), was a landmark U.S. Supreme Court case that established the principle of judicial review in the United States, meaning that American courts have the power to strike down laws and statutes that 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. The Court's landmark decision established that the U.S. Constitution is actual law, not just a statement of political principles and ideals, and helped define the boundary between the constitutionally separate executive and judicial branches of the federal government.

The case originated in early 1801 as part of the political and ideological rivalry between outgoing President John Adams and incoming President Thomas Jefferson. Adams had lost the U.S. presidential election of 1800 to Jefferson, and in March 1801, just two days before his term as president ended, Adams appointed several dozen Federalist Party supporters to new circuit judge and justice of the peace positions in an attempt to frustrate Jefferson and his supporters in the Democratic-Republican Party. The U.S. Senate quickly confirmed Adams' appointments, but upon Adams' departure and Jefferson's inauguration a few of the new judges' commissions still had not been delivered. Jefferson believed the undelivered commissions were void and instructed his Secretary of State, James Madison, not to deliver them. One of the undelivered commissions belonged to William Marbury, a Maryland businessman who had been a strong supporter of Adams and the Federalists. In late 1801, after Madison had repeatedly refused to deliver his commission, Marbury filed a lawsuit in the Supreme Court asking the Court to issue a writ of mandamus forcing Madison to deliver his commission.In an opinion written by Chief Justice John Marshall, the Court held firstly that Madison's refusal to deliver Marbury's commission was illegal, and secondly that it was normally proper for a court in such situations to order the government official in question to deliver the commission. But in Marbury's case, the Court did not order Madison to comply. Examining the section of the law Congress had passed that gave the Supreme Court jurisdiction over types of cases like Marbury's, Marshall found that it had expanded the definition of the Supreme Court's jurisdiction beyond what was originally set forth in the U.S. Constitution. Marshall then struck down that section of the law, announcing that American courts have the power to invalidate laws that they find to violate the Constitution. Because this meant the Court had no jurisdiction over the case, it could not issue the writ that Marbury had requested.