What principle was established by the Supreme Court case Marbury v. Madison (1803)?

The principle established by the Supreme Court case Marbury v. Madison (1803) is judicial review. This landmark decision asserted the power of the Supreme Court to declare laws and actions of Congress and the President unconstitutional. In this case, Chief Justice John Marshall articulated that it is the duty of the judicial system to interpret the law and ensure that no act is inconsistent with the Constitution. This effectively made the judiciary an equal branch of government, capable of checking the powers of the other branches.

Judicial review became a foundational aspect of American law, enabling the courts to uphold the Constitution as the supreme law of the land, and ensuring that both legislative and executive actions are subject to legal scrutiny. This case laid the groundwork for the balance of power in the federal government and has had a lasting impact on the relationship between the judiciary and the other branches of government.