EXAMPLE: Two parties litigate an issue in one federal disctrict court, and the defendant loses. Under the principle of res judicata, the defendant could not then go to another federal district court and litigate the same issue a second time.Source: Barron's Dictionary of Legal Terms, Steven H. Gifis, 5th Edition; ©
Compare collateral [COLLATERAL ESTOPPEL].
"Under the doctrine of res judicata, a judgment on the merits in a prior suit bars a second suit involving the same parties or their privies based on the same cause of action. Under the doctrine of collateral estoppel, on the other hand, the second action is upon a different cause of action, and the judgment in the prior suit precludes relitigation of issues actually litigated and necessary to the outcome of the first action."
"In this case, however, appellant has not litigated in the state court her sex discrimination claims, now stated as a Title VII action. Such claims were dismissed by the state court in order to permit a later federal court action. This is that action."