What principle did the Supreme Court assert in Marbury vs. Madison?

The principle asserted by the Supreme Court in Marbury vs. Madison is judicial review over acts of Congress. This landmark case, decided in 1803, established the critical function of the judiciary in reviewing and potentially invalidating laws passed by Congress that are found to be in conflict with the Constitution. The Court, led by Chief Justice John Marshall, determined that it is the duty of the judiciary to ensure that the law remains consistent with the foundational document of the United States, thus solidifying the judiciary's role as a co-equal branch of government and providing a mechanism for enforcing the rule of law.

This case set a precedent that allows courts to invalidate any legislation or executive action that they determine to be unconstitutional, thereby reinforcing the concept of checks and balances among the branches of government. The importance of this ruling continues to resonate in contemporary legal discussions regarding the limits of congressional power and the interpretation of constitutional principles.