Res Judicata Law and Legal Definition

Res judicata is a Latin term meaning "a thing decided". It is a common law doctrine meant to prevent relitigation of cases between the same parties regarding the same issues and preserve the binding nature of the court's decision. Once a final judgment has been reached in a lawsuit, subsequent judges who are presented with a suit that is identical to or substantially the same as the earlier one will apply the doctrine of res judicata to uphold the effect of the first judgment.

Res judicata does not prevent appeals to a higher court and there are limited exceptions to res judicata that allow a party to attack the validity of the original judgment in the same court. These exceptions--usually called collateral attacks--are typically based on procedural or jurisdictional issues, based on the lack of a court's authority or jurisdiction to issue the judgment.