Jury nullification (US/UK), jury equity (UK), or a perverse verdict (UK) occurs when the jury in a criminal trial gives a not guilty verdict regardless of whether they believe a defendant has broken the law. The jury's reasons may include the belief that the law itself is unjust, that the prosecutor has misapplied the law in the defendant's case, that the punishment for breaking the law is too harsh, or general frustrations with the criminal justice system. Some juries have also refused to convict due to their own prejudices in favor of the defendant. Such verdicts are possible because a jury has an absolute right to return any verdict it chooses.

Nullification is not an official part of criminal procedure, but is the logical consequence of two rules governing the systems in which it exists:

1. Jurors cannot be punished for passing an incorrect verdict.
2. In many jurisdictions, a defendant who is acquitted cannot be tried a second time for the same offence.

A jury verdict that is contrary to the letter of the law pertains only to the particular case before it. However, if a pattern of acquittals develops in response to repeated attempts to prosecute a particular offence, this can have the de facto effect of invalidating the law. Such a pattern may indicate public opposition to an unwanted legislative enactment. It may also happen that a jury convicts a defendant even if no law was broken, although such a conviction may be overturned on appeal. Nullification can also occur in civil trials, but (unlike in criminal trials) if the jury renders a not liable verdict that is clearly at odds with the evidence, the judge can issue a judgment notwithstanding the verdict, or order a new trial.