The general power of juries to decide on verdicts was recognised in the English Magna Carta of 1215, which put into words existing practices:
No free man shall be captured, and or imprisoned, or disseised of his freehold, and or of his liberties, or of his free customs, or be outlawed, or exiled, or in any way destroyed, nor will we proceed against him by force or proceed against him by arms, but by the lawful judgment of his peers, or by the law of the land.
Jury nullification is a finding by a trial jury in favour of the defendant, in contradiction to the jury's belief about the facts of the case. This may happen in both civil and criminal trials. In a civil trial, a jury nullifies by finding a defendant not liable, even though members of the jury may believe the defendant is liable. In a criminal trial, a jury nullifies by acquitting a defendant, even though the members of the jury may believe that the defendant did the illegal act, but they do not believe he/she should be punished for it. This may occur when members of the jury disagree with the law the defendant has been charged with breaking, or believe that the law should not be applied in that particular case. A jury can similarly unjustly and illegally convict a defendant on the ground of disagreement with an existing law, even if no law is broken (although in jurisdictions with double jeopardy rules, a conviction can be overturned on appeal, but an acquittal cannot)
Juries have also refused to convict due to the perceived injustice of a law in general, or of the way the law is applied in particular cases. There have also been cases where the jury has refused to convict due to their own prejudices, e.g. about the race of one of the parties in the case.
Jury nullification is the source of much debate. Some maintain that it is an important safeguard of last resort against wrongful imprisonment and government tyranny. Others view it as a violation of the right to a jury trial, which undermines the law. Some view it as a violation of the oath sworn by jurors. In the United States, some view the requirement that jurors take an oath to be unlawful in itself, while still others view the oath's reference to "deliverance" to require nullification of unjust law: "will well and truly try and a true deliverance make between the United States and the defendant at the bar, and a true verdict render according to the evidence, so help [me] God." United States v. Green, 556 F.2d 71 (D.C. Cir. 1977). Some fear that nullification could be used to permit violence against socially unpopular factions. They point to the danger that a jury may choose to convict a defendant who has not broken the letter of the law. However, judges retain the rights both to decide sentences and to disregard juries' guilty verdicts, acting as a check against malicious juries. Jury nullification may also occur in civil suits, in which the verdict is generally a finding of liability or lack of liability (rather than a finding of guilty or not guilty).