Judicial review is the power of courts, particularly the Supreme Court in the United States, to examine and determine whether actions taken by the legislative, executive, or administrative branches of government comply with the Constitution. If these actions are found to be inconsistent with the Constitution, they can be declared unconstitutional and thus null and void
. This power is not explicitly stated in the U.S. Constitution but is implied from its structure and principles, notably from Article III and Article VI. The landmark case establishing judicial review in the U.S. was Marbury v. Madison (1803), where Chief Justice John Marshall asserted that it is the judiciary's duty to interpret the law and invalidate laws that conflict with the Constitution
. Judicial review serves as a check on the legislative and executive branches, ensuring they do not exceed constitutional limits. It also applies to state laws and constitutions when they conflict with the federal Constitution
. While courts review the lawfulness and constitutionality of government actions, they generally do not substitute their judgment for that of the original decision-makers unless the actions violate legal or constitutional standards
. In summary, judicial review is a fundamental mechanism in constitutional law that upholds the supremacy of the Constitution by allowing courts to invalidate government actions that violate constitutional principles
