How can U.S. courts declare a law unconstitutional?

In the United States, courts declare laws unconstitutional through the doctrine of judicial review, a power established by the Supreme Court in the landmark case Marbury v. Madison (1803).12

This process functions according to the following principles:

• Cases and Controversies: U.S. federal courts do not provide advisory opinions. A constitutional question must be raised within the context of an actual "case or controversy" where the parties involved have a direct, personal interest.23
• Judicial Duty: Because the U.S. Constitution is the supreme law of the land, courts are obligated to interpret it. When a statute or executive action conflicts with constitutional provisions, the court must declare that act null and void.23
• Universal Application: While the U.S. Supreme Court is the ultimate arbiter, all lower courts in the United States are also empowered to determine the constitutionality of statutes or executive actions when such questions arise during litigation.3
• Political Questions: Courts generally avoid applying constitutional standards to "political questions"—issues they believe are better resolved by the legislative or executive branches—though this doctrine is not always a barrier to judicial intervention in sensitive matters.24