Double jeopardy is a legal protection in the United States Constitution that says you can't be tried twice for the same crime in the same court system. If you're accused of a crime and found not guilty in court, that court system can't just keep trying you over and over, hoping to get a different result. Once the jury says “not guilty,” that's final for that specific crime in that system. Even if new evidence appears later, prosecutors in that system usually can't bring you back to trial for that same crime.

This protection exists because it would be deeply unfair to let the government, with all its resources and power, keep prosecuting someone until it finally wins. Imagine if your teacher could keep testing you on the same material every day until you finally failed. That wouldn't measure what you know, it would just wear you down. The same principle applies in criminal trials: everyone deserves one fair chance to defend themselves, and then it's over.

The Fifth Amendment to the Constitution says no person shall “be subject for the same offense to be twice put in jeopardy of life or limb,” meaning you face that risk only once. This right applies only to criminal cases, not civil lawsuits. If a trial ends without a verdict (like a mistrial), prosecutors may be able to try again, because the case was never finished the first time.