The most important result of Marbury v. Madison, (1803), is that it affirmed the Supreme Court's right of judicial review and set a precedent for future cases. Judicial review is the power of the Court to evaluate challenged legislation to determine its constitutionality, and to nullify any laws they find unconstitutional.
In Marbury, the Supreme Court determined Section 13 of the Judiciary Act of 1789 was unconstitutional because Congress had overreached their authority by granting the Court the right to issue all writs of mandamus, which contradicted the language of Article III of the Constitution. This was also the first time the Supreme Court declared an Act of Congress unconstitutional.
