A jury is a sworn body of people (jurors) convened to hear evidence and render an impartial verdict (a finding of fact on a question) officially submitted to them by a court, or to set a penalty or judgment.

Juries developed in England during the Middle Ages and are a hallmark of the English common law system. As such, they are used by the United Kingdom, the United States, Canada, Ireland, Australia, and other countries whose legal systems were derived from the British Empire. Most other countries use variations of the European civil law or Islamic sharia law systems, in which juries are not generally used.

Most trial juries are "petit juries", and usually consist of twelve people. Historically, a larger jury known as a grand jury was used to investigate potential crimes and render indictments against suspects. All common law countries except the United States and Liberia have phased these out. The modern criminal court jury arrangement has evolved out of the medieval juries in England. Members were supposed to inform themselves of crimes and then of the details of the crimes. Their function was therefore closer to that of a grand jury than that of a jury in a trial.