The US Supreme Court serves several purposes, some of which were established in the Constitution, while others developed through practice over time.
The Court’s central role nowadays is as the final interpreter of federal law and the Constitution, resolving disputes about their meaning and delivering the final word on related questions. This was not entirely in the Court’s scope when it was established. This role developed from a landmark case, Marbury v. Madison (1803), in which the Supreme Court’s authority expanded to include “judicial review,” the power to strike down laws or executive actions that conflict with the Constitution. As Chief Justice John Marshall wrote at the time, "It is emphatically the province and duty of the judicial department to say what the law is."
The Supreme Court also serves as an umpire of sorts between government branches and its various levels. Article III gives the Court jurisdiction over disputes between the states, cases involving the federal government, and conflicts between federal and state law. It often functions as a referee when disagreements arise concerning the limits of power in Congress, the executive branch, and the states.
Additionally, the Court sometimes serves as a defender of individual rights. During the 20th century, it gradually incorporated most protections in the Bill of Rights against state and local governments through the Fourteenth Amendment’s Due Process Clause; since then, the Court has helped ensure state and federal governments do not take away individual liberties.
Most of its cases, however, come from its appellate jurisdiction, the authority to review the decisions of lower courts. The Supreme Court is the final appeals court in the federal system, meaning when appeals reach the high court, its ruling cannot be appealed again unless, of course, a constitutional amendment were to happen or the Court later reversed its decision.
Overall, the Supreme Court is the nation’s highest court and an important interpreter of the Constitution, ensuring that laws passed by Congress and actions by the president align with the nation's foundational rules.
