Jury nullification is a legal concept that occurs when a jury in a criminal trial returns a verdict of "not guilty" even if they believe beyond a reasonable doubt that the defendant broke the law. It is not an official part of criminal procedure, but is the logical consequence of two rules governing the systems in which it exists: jurors cannot be punished for passing an incorrect verdict, and in many jurisdictions, a defendant who is acquitted cannot be tried a second time for the same offense.

Jury nullification can 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. There are differing perspectives on the role and basis of jury nullification in American jurisprudence. Some view it as an important safeguard of last resort against wrongful imprisonment and government tyranny, while others view it as a violation of the right to a jury trial, which undermines the law.

Jury nullification is a discretionary act and is not a legally sanctioned function of the jury. As such, it is considered to be inconsistent with the jurys duty to return a verdict based solely on the law and the facts of the case, and counsel is not permitted to present the concept of jury nullification to the jury. However, there is a historical basis for jury nullification, and it may be seen as an integral feature of the birth of this nation.

Jury nullification may also be used to send messages to prosecutors about misplaced enforcement priorities or what jurors see as harassing or abusive prosecutions. While courts have taken steps to prevent jury nullification, it provides an important mechanism for feedback and prevents the criminal justice system from becoming too rigid.