Jeopardy is a defendant’s risk or danger of conviction when put on trial. Jeopardy does not exist until the jury is sworn in or until evidence is introduced. At common law, a defendant could be exposed to jeopardy for the same offense only once. The condition of exposing a person after he has once been convicted or acquitted of the offence charged by the verdict of a jury, and judgment has passed thereon for or against him is called double jeopardy. Double jeopardy is prohibited by the Fifth and Fourteenth amendments to the U.S. Constitution. However, a second trial is legal, if the first court had incompetent jurisdiction or if there was error in the proceedings or if the jury could not reach a verdict. Res judicata is a similar principle in civil proceedings.