Answer:
Marbury v. Madison was a U.S. Supreme Court case that established the principle of judicial review. This means that the Supreme Court has the power to declare acts of Congress unconstitutional if they violate the Constitution.
The case was brought to the court by William Marbury, who had been appointed a justice of the peace in the District of Columbia by President John Adams before Adams left office. However, the incoming Secretary of State, James Madison, refused to deliver Marbury's commission.
Marbury sued Madison, seeking a writ of mandamus, which would have compelled Madison to deliver the commission. The Supreme Court, under Chief Justice John Marshall, ruled that Marbury was entitled to the commission, but that the Judiciary Act of 1789, which had given the Court the power to issue writs of mandamus, was unconstitutional.
This decision established the principle of judicial review, which has since been used to strike down many federal and state laws that were deemed unconstitutional by the Supreme Court.