Appellate courts exist primarily to review and correct errors made in the primary or trial courts. While specific procedures might vary among the appellate court systems in the United States, these courts all perform that primary function. In addition, appellate courts deal with the development and application of law.
According to the Wisconsin Court System website, the primary purpose of an appellate court is to correct errors that occurred at the trial court level. To correct errors, an appellate court looks to "precedent," or the decisions in similar cases made before. A state appellate court is required to follow precedent set by a state's supreme court and the U.S. Supreme Court.
Development of Law
According to Cornell University's Legal Information Institute, appellate courts also have a duty to develop finer points of law. Arguments in appellate cases are usually made by attorneys and in written briefs, and focus on the law of the case. The facts in most cases are determined in the trial court, and the appellate court relies on the trial court's findings of fact when considering the law to apply to the case. The law-focused approach of an appellate court allows it to focus on the development of legal issues and themes rather than on the facts of a particular case.
Uniform Law Application
Cornell University's Legal Information Institute also notes that, along with its error-correcting and law-developing duties, an appellate court also serves an important role in monitoring the uniform application of law. Since a single appellate court usually takes cases from several different trial courts, it can ensure that trial courts in different places are nevertheless applying the same law in the same way. It can also clarify points of law that are confusing or misunderstood in the trial courts.