Res judicata (also known as claim preclusion) is a legal doctrine that prevents parties from relitigating claims that have already been resolved by a final judgment on the merits in a prior case involving the same parties (or their privies) and arising from the same transaction or occurrence. It promotes finality, judicial efficiency, and prevents inconsistent judgments.However, res judicata is not absolute. It can be defeated or held inapplicable in several key situations. These generally fall into two broad categories: (1) situations where the prior judgment does not qualify as a preclusive one, and (2) recognized exceptions or equitable grounds that allow relitigation despite an otherwise valid prior judgment.Situations Where Res Judicata Does Not Apply (Most Common Ways It Is “Defeated”)These occur when one or more core elements required for res judicata are missing:
- No final judgment on the merits in the prior case.
Res judicata only applies to judgments that resolve the case substantively. Examples that do not trigger preclusion (unless the court explicitly says otherwise) include:- Dismissals for lack of jurisdiction
- Dismissals for improper venue
- Dismissals for failure to join a required party
- Voluntary dismissals
- Dismissals expressly “without prejudice”
- The prior court lacked jurisdiction (subject-matter, personal, etc.).
A judgment from a court without competent jurisdiction has no preclusive effect. - Different parties (or no privity between the parties in the two cases).
- Different claims / causes of action — i.e., the new claim does not arise from the same transaction, occurrence, or nucleus of operative facts as the prior case.
(Note: Under the modern “transactional” test used in most U.S. jurisdictions, this is a high bar — claims that could have been raised in the first case are usually barred.) - The prior judgment was not final (e.g., still subject to appeal or interlocutory).
- Continuing wrongs or new, independent breaches (e.g., a new breach of contract after the first lawsuit, or ongoing violations like a continuing nuisance).
Narrow Exceptions / Collateral Attacks (Even When Elements Are Met)In limited circumstances, courts may allow a collateral attack on the prior judgment or refuse to apply res judicata to avoid injustice:
- Fraud, collusion, or extrinsic fraud in obtaining the prior judgment (e.g., perjured testimony or concealed evidence that prevented a fair trial).
- Lack of a full and fair opportunity to litigate the claim or issue in the prior proceeding (a due process concern, sometimes raised in federal habeas or § 1983 contexts after state-court judgments).
- Newly discovered evidence that could not have been obtained earlier with reasonable diligence (very rare, jurisdiction-dependent, and often requires a motion to vacate rather than a new suit).
- Violation of fundamental / constitutional rights (more common in some non-U.S. systems or specific U.S. constitutional challenges).
- Declaratory judgment exception — a declaratory action typically only precludes what it actually decides, not every potential related claim.
Res judicata is an affirmative defense — the party asserting it must plead and prove it. Courts apply it rigidly in most cases but will not do so if it would produce manifest injustice in exceptional situations.The exact scope and exceptions can vary by jurisdiction (federal vs. state courts, and among states), so the controlling law of the relevant forum matters. In U.S. federal courts, the principles are largely governed by Federal Rules of Civil Procedure and Supreme Court precedents.
Supreme Court Cases – Res Judicata and Collateral Estoppel
Cromwell v. County of Sac (94 U.S. 351, 1876)
This early foundational case distinguished between res judicata (claim preclusion) and collateral estoppel (issue preclusion). It established that a prior judgment bars relitigation of the same claim but only precludes issues actually litigated and determined when raised in a different claim. It remains a cornerstone for understanding the scope of preclusion doctrines.Durfee v. Duke (375 U.S. 106, 1963)
The Court held that a state court’s determination of its own jurisdiction (in a fully litigated in rem proceeding) is entitled to full faith and credit and res judicata effect in other states, preventing collateral attacks on jurisdiction except in narrow circumstances. This reinforced the finality of judgments involving jurisdictional issues.Allen v. McCurry (449 U.S. 90, 1980)
The Court ruled that collateral estoppel (issue preclusion) applies in § 1983 civil rights actions to issues actually litigated and decided in prior state-court proceedings, promoting respect for state judgments under full faith and credit principles.Migra v. Warren City School District Board of Education (465 U.S. 75, 1984)
Extending Allen, the Court held that claim preclusion (res judicata) also applies in § 1983 cases. Federal courts must give a prior state-court judgment the same preclusive effect it would receive in the rendering state’s courts, rejecting “claim-splitting” between state and federal forums.Semtek International Inc. v. Lockheed Martin Corp. (531 U.S. 497, 2001)
A key modern case on federal diversity judgments. The Court clarified that the claim-preclusive effect of a federal court’s dismissal “on the merits” (e.g., based on a state statute of limitations) in a diversity action is governed by federal common law, which incorporates the preclusion rules of the state where the federal court sits (rather than a uniform federal rule). This resolved forum-shopping concerns and harmonized treatment of state-law claims.Lucky Brand Dungarees, Inc. v. Marcel Fashions Group, Inc. (592 U.S. 95, 2020)
The Court addressed whether res judicata/claim preclusion extends to “defense preclusion” (barring a defense that could have been raised earlier). It rejected a broad application in this trademark dispute, holding that claim preclusion generally bars relitigation of claims (not defenses) arising from the same transaction or nucleus of operative facts, and declined to recognize defense preclusion here. The decision narrowed expansive lower-court views on precluding defenses.
