The United States Supreme Court is the ultimate court of last resort. While the cases heard by lower level trial courts and appellate courts can be appealed to state supreme courts and federal appellate courts, no other court looks over the shoulder of the U.S. Supreme Court. The opinions issued by the nine justices on this court are final.
Every year the U.S. Supreme Court receives thousands of requests to have the high court hear specific cases. Experts estimate that roughly 5000 requests are made annually. These requests, called petitions for writs of certiorari, are essentially pleas stating, "please hear my case." Each justice on the U.S. Supreme Court has a number of skilled law clerks working for him or her and these clerks review every petition for writ of certiorari and submit a "cert memo" regarding the writs they review to the justice they are assigned. The judges review the memos and hold a conference to determine which of these cases should go on the court's docket.
The "Rule of Four" controls matters when deciding which issues the high court will hear. If four justices agree that a specific petition for writ of certiorari should be granted, then the case will be placed on the Court's docket and an order stating that certiorari has been granted will be issued to the petitioner.
Typically, the justices grant certiorari, or "cert" as it is commonly called, to cases which may have far-reaching, interesting issues. The court may wish to hear a case and issue its opinion so that it can offer guidance to the lower level judges throughout the country who have the same issues come through their courtrooms on a daily basis. Cert is also often granted when there is a conflict among a number of lower level trial or appellate courts in interpreting a rule of law or a prior judicial decision. In such cases, the Supreme Court will issue an order specifying the correct interpretation of the law to pave the way and set the legal precedent for the lower courts.