What was established by the landmark case Marbury v. Madison?

The landmark case of Marbury v. Madison, decided in 1803, is significant for establishing the principle of judicial review, which allows the Supreme Court to evaluate the constitutionality of legislative and executive actions. This case arose when William Marbury petitioned the Supreme Court for a writ of mandamus, seeking to compel Secretary of State James Madison to deliver his commission as a justice of the peace. Chief Justice John Marshall concluded that while Marbury had a right to his commission, the court did not have the power to issue the writ because the relevant portion of the Judiciary Act of 1789 was unconstitutional.

This ruling was monumental because it confirmed the Supreme Court's authority to nullify laws that it found to violate the Constitution, effectively asserting the judiciary's role as a co-equal branch of government. As a result, judicial review has become a fundamental aspect of American law, enabling the judiciary to serve as a check on both the legislative and executive branches.