In law, an appeal is the process in which cases are reviewed by a higher authority, where parties request a formal change to an official decision. Appeals function both as a process for error correction as well as a process of clarifying and interpreting law. Although appellate courts have existed for thousands of years, common law countries did not incorporate an affirmative right to appeal into their jurisprudence until the 19th century.

"Appellate review" is the general term for the process by which courts with appellate jurisdiction exercise jurisdiction over matters decided by lower courts. It is distinguished from judicial review, which refers to the court's overriding constitutional or statutory right to determine whether a legislative act or administrative decision is defective for jurisdictional or other reasons (which may vary by jurisdiction).

American English and British English have diverged significantly on the topic of appellate terminology. American cases go up "on appeal" and one "appeals from" (intransitive) or "appeals" (transitive) an order, award, judgment, or conviction, while decisions of British courts are said to be "under appeal" and one "appeals against" a judgment. An American court disposes of an appeal with words like "judgment affirmed" (the appeal is without merit) or "judgment reversed" (the appeal has merit), while a British court disposes of an appeal with words like "appeal dismissed" (the appeal is without merit) or "appeal allowed" (the appeal has merit).

In most jurisdictions the normal and preferred way of seeking appellate review is by filing an appeal against the lower court's judgment.

Appellate courts and other systems of error correction have existed for many millennia. During the first dynasty of Babylon, Hammurabi and his governors served as the highest appellate courts of the land. Ancient Roman law recognized the right to appeal in the Valerian and Porcian laws since 509 BC. Later it employed a complex hierarchy of appellate courts, where some appeals would be heard by the emperor. Additionally, appellate courts have existed in Japan since at least the Kamakura shogunate (1185–1333). During this time, the shogunate established hikitsuke, a high appellate court to aid the state in adjudicating lawsuits.

Although some scholars argue that "the right to appeal is itself a substantive liberty interest", the notion of a right to appeal is a relatively recent advent in common law jurisdictions. Commentators have observed that common law jurisdictions were particularly "slow to incorporate a right to appeal into either its civil or criminal jurisprudence".

The idea of an appeal from court to court (as distinguished from court directly to the Crown) was unheard of in early English courts. English common law courts eventually developed the writs of error and certiorari as routes to appellate relief, but both types of writs were severely limited in comparison to modern appeals in terms of availability, scope of review, and remedies afforded. For example, writs of error were originally not available as a matter of right and were issued only upon the recommendation of the attorney general (which was initially discretionary but by modern times was regularly granted). Certiorari was originally available only for summary offences; in the early 19th century, certiorari became available for indictable offences, but only to obtain relief before judgment. Due to widespread dissatisfaction with writs (resulting in the introduction of at least 28 separate bills in Parliament), England switched over to appeals in civil cases in 1873, and in criminal cases in 1907.

We are not final because we are infallible, but we are infallible only because we are final.