Marbury v. Madison is a landmark case in United States Supreme Court history, widely considered to be the most influential and important decision ever made by the court. The case established an early precedent for judicial review of legislation passed by Congress, giving the courts authority to declare laws unconstitutional if they conflict with higher law, such as the U.S. Constitution or other federal statutes. This power would later become known as "judicial supremacy" and has been a major factor in shaping American democracy since its inception in 1803.
The case arose from President John Adams' last-minute appointments to various government offices on his way out of office after losing re-election in 1800 to Thomas Jefferson's Democratic-Republican Party. William Marbury was among those appointed but never received his commission due to political infighting between Adams' Federalist party and Jefferson's incoming administration; he then sued Secretary of State James Madison over it (hence why it became known as Marbury v. Madison). In their ruling, Chief Justice John Marshall wrote that while technically Marbury had a right to receive his commission, because there was no statute authorizing the issuance of writs of mandamus—a legal order forcing someone like Madison to perform some act—the judiciary could not intervene on behalf of Marbury even though they agreed he should have gotten what he wanted: this set forth judicial review and gave judges more control over how laws were interpreted than any other court. The previous ruling had been done before then.