In civil litigation, most lawsuits are resolved by the voluntary agreement (settlement) of the parties (litigants) before the judge, jury, or arbitrator decides how the case should be resolved. But if a case goes to trial and the judge or jury decides how the case should be resolved, one or more parties to the lawsuit may appeal that decision to a higher court—usually a court of appeals, whether in the state court system or the federal court system.

And one or more of the parties who are dissatisfied with the decision of the court of appeals generally may ask the highest court in the jurisdiction (state court or federal court) to review the decision of the lower court(s). The highest court in the state court system is often called the supreme court—but in some states it has a different name—for example, in New York it is called the New York Court of Appeals. And in the federal court system the highest court is the United States Supreme Court.

There are different standards by which higher courts review the decisions of lower courts, and these are known as standards of review. In many cases appellate courts are required to give deference to the decision made by the jury or the lower court. These decisions are reviewed for an abuse of discretion, and the higher court will only reverse the lower court’s decision if it determines the lower court abused its discretion. And in some states certain decisions made by the lower court or the jury are reviewed using a substantial evidence standard, and the question for the higher court is whether there is substantial evidence to support the decision of the lower court or the jury. Finally, some decisions are reviewed without giving deference to the decision made by the jury or the lower court, and this standard of review is called de novo review.

Similarly, in criminal prosecutions, the prosecution (state or federal government) or the defendant (person or entity) may generally appeal the decision of the jury or judge to the intermediate appellate court (often the court of appeals), and ultimately to the highest court (often the state supreme court, or the U.S. Supreme Court, or other court of last resort).

In Illinois, civil litigation often concludes with a settlement between the parties before a trial is necessary. However, if a case does go to trial and a decision is rendered by a judge or jury, the losing party has the right to appeal to a higher court. The first level of appeal is typically to the Illinois Appellate Court. If a party is still dissatisfied with the outcome, they may request a review by the Illinois Supreme Court, which is the highest court in the state's judicial system. Similarly, in the federal system, the ultimate court of appeal is the United States Supreme Court. The standards of review used by appellate courts in Illinois include 'abuse of discretion,' 'substantial evidence,' and 'de novo.' An 'abuse of discretion' standard means the appellate court will only overturn the lower court's decision if it was unreasonable or arbitrary. The 'substantial evidence' standard requires the appellate court to determine if there is enough evidence to support the lower court's decision. 'De novo' review allows the appellate court to consider the matter afresh, without giving deference to the lower court's findings. These standards also apply in criminal cases, where either the prosecution or the defense can appeal to higher courts following a trial decision.