What does the judicial branch do?

The judicial branch interprets federal laws, decides cases involving federal law and the Constitution, and reviews the constitutionality of federal and state laws. Article III of the Constitution gives the federal judiciary the judicial Power of the United States and lists the specific kinds of cases federal courts can hear. These include cases arising under the Constitution or federal laws, cases involving foreign ambassadors, disputes between states, disputes between citizens of different states, and admiralty and maritime cases.

Federal courts apply law to facts to resolve disputes. They do not write laws (that is Congress's job) or enforce them (that is the executive branch's job), but their interpretations shape how laws actually function in practice. When a court rules on what a statute means, that ruling becomes binding precedent for similar cases in the future.

The most important power of the federal courts is judicial review, the authority to declare federal or state laws unconstitutional. The Supreme Court established this power in Marbury v. Madison (1803), in which Chief Justice John Marshall held that it is emphatically the province and duty of the judicial department to say what the law is. If a law conflicts with the Constitution, the courts must follow the Constitution.

Federal courts also interpret the Constitution itself. The Supreme Court has issued hundreds of major rulings over more than two centuries on what specific constitutional provisions mean. These include rulings on the Bill of Rights, the powers of Congress, the powers of the President, the rights of states, and the meaning of equal protection and due process.

The federal judiciary handles four broad categories of cases. Criminal cases prosecute violations of federal law, such as bank robbery, drug trafficking, and tax evasion. Civil cases involve disputes between private parties or between private parties and the government, ranging from civil rights claims to contract disputes to constitutional challenges. Bankruptcy cases handle debt restructuring under federal bankruptcy law. Appellate cases review decisions of lower courts.

The Supreme Court sits at the top, with the Chief Justice and eight Associate Justices reviewing roughly 60 to 80 cases per term out of more than 7,000 petitions filed each year.