A final court of appeal. The best‐known example is the United States Supreme Court; there are also American state supreme courts, although in some cases they are named differently. Article III of the US Constitution provides for a supreme court at the apex of the federal judiciary while leaving to Congress the establishment of lower federal courts. The number of US Supreme Court justices has varied between five and ten, but has remained at nine since 1869. Justices are appointed by the President with the advice and consent of the Senate. These are lifetime appointments subject to good behaviour. Only one Supreme Court judge has ever been impeached, and he was acquitted, in 1805. The original jurisdiction of the Court is very narrow in scope and it operates almost entirely as a court of appeal. Principally through its exercise of judicial review the Supreme Court, from time to time, appears to assume great power and to become effectively a maker of public policy. However, the Court is also constrained by the checks and balances of the Constitution. Thus the appellate jurisdiction of the Supreme Court is determined by act of Congress, as is the structure of the federal judiciary and the number of federal judges. The Court has no means of enforcing its decisions. As Alexander Hamilton observed in The Federalist, no. 78, the federal judiciary is the ‘least dangerous’ branch, possessing ‘neither force nor will but merely judgment; and must ultimately depend upon the aid of the executive arm for the efficacy of its judgments’.
In the United Kingdom the court of final appeal (supreme court in the general sense) is the House of Lords in its judicial capacity; but the Supreme Court as defined by the Judicature Act 1873 comprises the High Court and the Court of Appeal. In order to more clearly separate the role of the House of Lords as a legislative and judicial body, the Constitutional Reform Act 2005 provided for the creation of a new UK Supreme Court, due to start work in October 2009. It will assume the jurisdiction of the current Appellate Committee of the House of Lords and the devolution jurisdiction of the Judicial Committee of the Privy Council.
http://www.supremecourtus.gov/ United States Supreme Court site, including Constitutional background and information on rulings.