Res judicata is the generic term for a group of related concepts concerning the conclusive effects given final judgments. Within this general doctrine there are two principal categories: (1) claim preclusion—also known as res judicata; and (2) issue preclusion—also known as collateral estoppel.

These legal doctrines generally preclude litigants from relitigating claims and issues that were previously litigated to a final resolution or judgment.

In Louisiana, res judicata, also known as claim preclusion, prevents a party from re-litigating a claim that has already been finally adjudicated by a competent court. This means that once a court has rendered a final judgment on the merits of a case, the same parties cannot bring a subsequent lawsuit based on the same cause of action. Issue preclusion, also known as collateral estoppel, bars the re-litigation of specific issues that were actually litigated and essential to the judgment in a prior action between the same parties. Under Louisiana law, for res judicata to apply, the judgment must be valid, final, and rendered on the merits; the parties must be the same in both actions; and the cause of action in the second lawsuit must be the same as the one in the first. For collateral estoppel to apply, the issue must have been actually litigated, the determination of the issue must have been essential to the prior judgment, and the party against whom the doctrine is being asserted must have been a party or in privity with a party to the prior adjudication. These principles are codified in the Louisiana Code of Civil Procedure and are consistent with the state's interest in judicial efficiency and finality of judgments.