Res judicata is a Latin term used in the legal community, meaning “the thing has been decided.” It is used to refer to cases which cannot be appealed or retried. For example, if person X sues person Y for damages in California and damages are awarded by the court, the case cannot be repeated in Oregon. Res judicata is designed to ensure that cases are not tried again and again, clogging the legal system and potentially costing vast amounts of money.

When res judicata is invoked, it means that a case cannot be appealed or tried again in new courts. Because the appeals process is an important part of many legal systems, there are therefore a number of criteria which are considered before a judge decides to invoke res judicata. As a general rule, it must be proved that a verdict in the exact same case has already been obtained in a qualified court. In the event that a case is tried again because those involved were unaware that it had already been to court, the most recent verdict is typically considered to be the binding one.

There are a number of reasons why res judicata is important. In the first place, it ensures that people cannot be taken to court over and over again for the same thing: once a verdict is reached in a suit, it is considered final. It also reduces the risk of conflicting verdicts, or litigation which drags on for years. From the point of view of the legal system, res judicata keeps the system leaner and more efficient by allowing judges to throw out cases which have already been tried and judged.

There are circumstances in which a case may be tried again, by different litigants, for example, or because radically new evidence has emerged. This is common in suits against manufacturers, who may face a multitude of suits asking for damages as a result of faulty products. A case may also be challenged on the basis of the competency of the court, with lawyers arguing that although the case has already been judged, it was not judged in appropriate circumstances, and it should therefore be tried again.

This concept is handled slightly differently in various legal systems, with notable restrictions in legal systems based on civil law, while common law systems tend to be more forgiving. In civil law, cases must be fundamentally identical before they can be rejected on the basis of res judicata, while in common law, cases merely need to bear a substantial number of similarities. Common law judges look at whether or not the issues in the claim have already been decided in a competent court, and they examine previous cases to see whether or not claims have been awarded.