What legal principle was established by the Supreme Court case Marbury v. Madison?

The legal principle established by the Supreme Court case Marbury v. Madison is judicial review. This landmark decision, rendered in 1803, was pivotal in defining the ability of the Supreme Court to evaluate and invalidate laws or actions by Congress and the Executive that are found to be in conflict with the Constitution.

The case arose when William Marbury petitioned the Supreme Court for a writ of mandamus to compel Secretary of State James Madison to deliver his commission as a justice of the peace. Chief Justice John Marshall's ruling concluded that while Marbury was entitled to his commission, the Court did not have the authority to issue the writ because the section of the Judiciary Act of 1789 that granted the Supreme Court that power was itself unconstitutional. This assertion marked the first time the Supreme Court declared an act of Congress unconstitutional, thereby establishing the principle of judicial review.

This principle is fundamental as it allows the judiciary to serve as a check on legislative and executive powers, ensuring that no laws or actions contravene the Constitution. Judicial review has become a core function of the American legal system, reinforcing the role of the courts in upholding constitutional governance.