The Supreme Court of the United States is the highest court in the land and the only part of the federal judiciary specifically required by the Constitution.
The Constitution does not stipulate the number of Supreme Court Justices; the number is set instead by Congress. There have been as few as six, but since 1869 there have been nine Justices, including one Chief Justice. All Justices are nominated by the President, confirmed by the Senate, and hold their offices under life tenure. Since Justices do not have to run or campaign for re-election, they are thought to be insulated from political pressure when deciding cases. Justices may remain in office until they resign, pass away, or are impeached and convicted by Congress.
The Court's caseload is almost entirely appellate in nature, and the Court's decisions cannot be appealed to any authority, as it is the final judicial arbiter in the United States on matters of federal law. However, the Court may consider appeals from the highest state courts or from federal appellate courts. The Court also has original jurisdiction in cases involving ambassadors and other diplomats, and in cases between states.
Although the Supreme Court may hear an appeal on any question of law provided it has jurisdiction, it usually does not hold trials. Instead, the Court's task is to interpret the meaning of a law, to decide whether a law is relevant to a particular set of facts, or to rule on how a law should be applied. Lower courts are obligated to follow the precedent set by the Supreme Court when rendering decisions.
In almost all instances, the Supreme Court does not hear appeals as a matter of right; instead, parties must petition the Court for a writ of certiorari. It is the Court's custom and practice to "grant cert" if four of the nine Justices decide that they should hear the case. Of the approximately 7,500 requests for certiorari filed each year, the Court usually grants cert to fewer than 150. These are typically cases that the Court considers sufficiently important to require their review; a common example is the occasion when two or more of the federal courts of appeals have ruled differently on the same question of federal law.
If the Court grants certiorari, Justices accept legal briefs from the parties to the case, as well as from amicus curiae, or "friends of the court." These can include industry trade groups, academics, or even the U.S. government itself. Before issuing a ruling, the Supreme Court usually hears oral arguments, where the various parties to the suit present their arguments and the Justices ask them questions.
If the case involves the federal government, the Solicitor General of the United States presents arguments on behalf of the United States. The Justices then hold private conferences, make their decision, and (often after a period of several months) issue the Court's opinion, along with any dissenting arguments that may have been written.