res judicata

Res judicata is a Latin phase that translates to “a matter judged.” It is the principle that a cause of action may not be relitigated once there has been a final judgment on the merits. In this context, “finality” refers to a court’s rendering of such a judgment.

Res judicata is also called claim preclusion, and the terms are used interchangeably.

Bar and Merger

Claim preclusion has two main applications:

Bar: A losing plaintiff cannot sue the same defendant again on the same cause of action. Example: Plaintiff P sues Defendant D on Cause of Action C and loses. P may not bring another suit against D on C.

Merger: A winning plaintiff cannot sue the same defendant again on the same cause of action to obtain additional recovery. Example: P wins against D on C but may not file a new action against D on C to seek more damages.

A claim can have finality even if no damages are awarded. A prevailing party who believes damages were inadequate, or who received none, cannot bring another suit on the same cause of action.

Policies Behind Claim Preclusion

Courts uphold claim preclusion to:

promote judicial efficiency
ensure fairness
avoid inconsistent judgments

Judgments Not “On the Merits”

Historically, claim preclusion applied only to decisions on the merits; meaning those based on law and fact after evidence is heard. The modern view in most jurisdictions includes certain dismissals, such as those for failure to state a claim under Federal Rule of Civil Procedure 12(b)(6).

Under Federal Rule of Civil Procedure 41(b), the following are not adjudications on the merits and are not claim-preclusive unless the order states otherwise:

lack of jurisdiction
improper venue
failure to join a required party under Rule 19
voluntary dismissals
dismissals expressly “without prejudice”

Many jurisdictions also treat dismissal for failure to prosecute as claim-preclusive, subject to appellate review for abuse of discretion.

Counterclaims

Rule 13 of the Federal Rules of Civil Procedure governs counterclaims. Generally, claim preclusion applies to unasserted compulsory counterclaims but not to unasserted permissive counterclaims. Two exceptions exist:

The defendant was unaware that the claim was compulsory (See: Dindo v. Whitney, 1971).
The defendant prevails on an affirmative defense and later counterclaims on the same facts.

Some jurisdictions follow the Common Law Compulsory Counterclaim Rule, barring a later claim if granting relief would nullify a prior judgment.

Other Doctrines with Similar Effect

Estoppel: A party cannot litigate a position inconsistent with earlier conduct on which another party detrimentally relied.

Judicial estoppel: A party cannot take factual positions in current litigation that contradict positions taken in earlier judicial proceedings.

Adverse Parties

Claim preclusion applies only to adverse parties, not to co-parties. By contrast, collateral estoppel (issue preclusion) can apply to both.

[Last reviewed in August of 2025 by the Wex Definitions Team]

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