Principal among these is the jury which, at the option of the litigants, functions in both civil and criminal cases. The jury is a group of citizens, traditionally 12 in number, summoned at random to determine the facts in a lawsuit. When a trial by jury is held, the judge will instruct the jury on the law, but it remains for the jury to decide the facts. This means that ordinary citizens will decide which party will prevail in a civil case, and whether, in a criminal case, the accused is guilty or innocent of the charge against him or her. The institution of the jury has had an important shaping effect on the common law.
Emphasis is on the oral testimony of witnesses, although documents also are presented as evidence.
Lawyers, acting as adversaries, take the lead in questioning the witnesses at trial, while the judge acts essentially as a referee. Testimony is recorded verbatim by a court reporter or electronically. Generally speaking, appeals courts confine their review of the lower court record to errors of law, not of fact. No new evidence is received on appeal. All this stands in marked contrast to what is usually found in civil law systems, where jury trials are for the most part unknown.