A Mistrial is a trial that a judge cancels prior to the return of a verdict.

A mistrial may be declared due to:

• The court determining that it lacks jurisdiction over a case
• Evidence being admitted improperly
• Misconduct by a party, a juror or an outside actor preventing a fair trial
• A hung jury which cannot reach a verdict with the required degree of unanimity
• Disqualification of a juror after the jury is impanelled, unless an alternate juror is available or the litigants agree to proceed with the remaining jurors.

Declaration of a mistrial means another trial must be held in the same matter: one important exception under the United States Constitution is that in criminal cases, if a mistrial was erroneously declared by the court, or if a mistrial was the result of prosecutorial misconduct that had the effect of "goading" the defendant into moving for it, then a retrial is barred by the protection against double jeopardy and the prosecution is terminated.