402 U.S. 313 (1971) (U.S. Supreme Court)
Blonder-Tongue Laboratories v. University of Illinois Foundation is a cornerstone of modern preclusion doctrine and a pivotal case in patent litigation.
Whether a patentee is precluded from relitigating the validity of a patent against a new defendant after a prior final adjudication of invalidity, where the patentee had a full and fair opportunity to litigate the issue in the earlier action.
Defensive nonmutual collateral estoppel permits a new defendant to prevent a plaintiff from relitigating an issue the plaintiff previously lost, when the plaintiff had a full and fair opportunity to litigate that issue and the prior judgment is final and on the merits; mutuality is not required. In patent cases, a prior final judgment that a patent is invalid may preclude the patentee from relitigating validity against different defendants, subject to fairness-based exceptions.
The Supreme Court held that mutuality is not required for defensive collateral estoppel in patent validity cases. A patentee who has previously lost on validity may be estopped from relitigating that issue against a new defendant if the patentee had a full and fair opportunity to litigate earlier. The judgment below was vacated and remanded to determine whether those conditions were met.
Blonder-Tongue is a landmark in both civil procedure and patent law. It established that defensive nonmutual collateral estoppel can bar a patentee from relitigating validity after a prior final invalidity judgment, ending the patentee's ability to take multiple bites at the apple against new defendants. For law students, the case is a foundational illustration of the transition from mutuality to a fairness-centered preclusion regime and a prime example of policy-driven judicial lawmaking aimed at conserving resources and preventing inconsistent judgments. The decision also shaped modern patent practice by encouraging consolidation of key validity disputes and reducing the leverage of patents previously adjudicated invalid. Although Blonder-Tongue focused on defensive use of nonmutual estoppel, it foreshadowed later developments, including Parklane Hosiery's recognition of limited offensive nonmutual collateral estoppel, and it continues to inform courts' fairness analyses in applying issue preclusion across diverse substantive areas.