In law, an appeal is the process in which cases are reviewed, 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.^[2] 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.^[3]

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.^[4] Ancient Roman law employed a complex hierarchy of appellate courts, where some appeals would be heard by the emperor.^[5] Additionally, appellate courts have existed in Japan since at least the Kamakura Shogunate (1185–1333 CE). During this time, the Shogunate established hikitsuke, a high appellate court to aid the state in adjudicating lawsuits.^[6] In the Eighteenth century, William Blackstone observed in his Commentaries on the Laws of England that appeals existed as a form of error correction in the common law during the reign of Edward III of England.^[7]

Although some scholars argue that "the right to appeal is itself a substantive liberty interest",^[8] the notion of a right to appeal is a relatively recent advent in common law jurisdictions.^[9] In fact, commentators have observed that common law jurisdictions were particularly "slow to incorporate a right to appeal into either its civil or criminal jurisprudence".^[10] For example, the United States first created a system of federal appellate courts in 1789,^[1] but a federal right to appeal did not exist in the United States until 1889, when Congress passed the Judiciary Act to permit appeals in capital cases.^[16] Two years later, the right to appeals was extended to other criminal cases, and the United States Courts of Appeals were established to review decisions from district courts.^[17] Some states, such as Minnesota, still do not formally recognize a right to criminal appeals.^[18]

Although some courts permit appeals at preliminary stages of litigation, most litigants appeal final orders and judgments from lower courts.^[20] A fundamental premise of many legal systems is that appellate courts review questions of law de novo, but appellate courts do not conduct independent fact-finding.^[21] Instead, appellate courts will generally defer to the record established by the trial court, unless some error occurred during the fact-finding process.^[22] Many jurisdictions provide a statutory or constitutional right for litigants to appeal adverse decisions.^[23] However, most jurisdictions also recognize that this right may be waived. In the United States, for example, litigants may waive the right to appeal, as long as the waiver is "considered and intelligent".^[24]

The appellate process usually begins when an appellate court grants a party's petition for review or petition for certiorari.^[25] Unlike trials, appeals are generally presented to a judge, or a panel of judges, rather than a jury.^[26] Before making any formal argument, parties will generally submit legal briefs in which the parties present their arguments.^[27] Appellate courts may also grant permission for an amicus curiae to submit a brief in support of a particular party or position.^[28] After submitting briefs, parties often have the opportunity to present an oral argument to a judge or panel of judges.^[29] During oral arguments, judges often ask question to attorneys to challenge their arguments or to advance their own legal theories.^[30] After deliberating in chambers, appellate courts will issue formal opinions that resolve the legal issues presented for review.^[31]

When considering cases on appeal, appellate courts generally affirm, reverse, or vacate the decision of a lower court.^[32] Some courts maintain a dual function, where they consider both appeals as well as matters of "first instance".^[33] For example, the Supreme Court of the United States primarily hears cases on appeal but retains original jurisdiction over a limited range of cases.^[34] Some jurisdictions maintain a system of intermediate appellate courts, which are subject to the review of higher appellate courts.^[35] The highest appellate court in a jurisdiction is sometimes referred to as a "court of last resort".^[36]