Preclusion and Finality Doctrines

Preclusion and finality doctrines are the family of common law civil procedure rules that stop parties from relitigating matters a court has already resolved. Claim preclusion, traditionally called res judicata, bars a party from bringing a second lawsuit on the same cause of action once a court has entered a final judgment on the merits. Issue preclusion, historically known as collateral estoppel and enforced against a party's own prior inconsistent position through judicial estoppel, instead bars relitigating a specific factual or legal issue that was actually decided in an earlier proceeding, even inside a different claim. The law of the case doctrine extends this same finality logic within a single lawsuit, holding that a ruling a trial court makes and that a party does not challenge on appeal binds every later stage of that same litigation absent new evidence, a change in controlling law, or clear error. Together these doctrines protect litigants from being forced to defend the same dispute twice and let courts and parties rely on a judgment once it is final.