## Facts

- The University of Illinois Foundation owned by assignment a patent covering “frequency independent unidirectional” television antennas.
- The Foundation sued Winegard Co. for infringement in federal court; that court held the patent invalid as obvious, and the judgment was affirmed on appeal.
- In a separate infringement action against a different party, a customer of Blonder-Tongue, Blonder-Tongue intervened and sought a declaration of invalidity.
- The Illinois federal court refused to treat the earlier invalidity judgment as preclusive, upheld the patent as valid, and found infringement.
- The court of appeals affirmed, applying then-governing doctrine requiring mutuality of estoppel in this setting.

## Issues

1. Whether a patentee may relitigate patent validity against different defendants after a final judgment has held the patent invalid.
2. Whether nonmutual defensive collateral estoppel may bar a patentee from relitigating validity when the patentee previously litigated and lost the validity issue.
3. What limitations, including “full and fair opportunity to litigate,” govern use of nonmutual estoppel based on an earlier invalidity judgment.

## Decision

- The Supreme Court overruled prior doctrine to the extent it barred an accused infringer from pleading estoppel based on a prior final judgment of patent invalidity.
- The Court held that a defendant may invoke nonmutual defensive collateral estoppel to prevent relitigation of patent validity if the patentee had a full and fair opportunity to litigate validity in the earlier case.
- The Court vacated the judgment and remanded to allow the parties to amend pleadings and develop a record on whether estoppel should apply under the new standard.

## Legal Principles

- Mutuality is not required for defensive collateral estoppel when the party to be estopped previously litigated the identical issue and lost.
- A final judgment holding a patent invalid may preclude the patentee from asserting validity in later infringement litigation against different defendants.
- Preclusion is not automatic; application depends on whether the patentee had a full and fair opportunity to litigate validity in the first action.
- In evaluating “full and fair opportunity,” courts may consider procedural adequacy, incentives to litigate, and whether the patentee lacked access to critical evidence or controlling legal standards in the earlier case.
- Limiting repeat validity litigation serves fairness and efficiency by reducing inconsistent judgments and avoiding the burden of defending against patents already adjudicated invalid.

## Conclusion

The Court permitted nonmutual defensive collateral estoppel in patent cases, allowing accused infringers to bar a patentee from relitigating validity after a prior final invalidity judgment, so long as the patentee previously had a full and fair opportunity to litigate the issue; the case was remanded for that determination.


Blonder-Tongue Laboratories, Inc. v. University of Illinois Foundation, 402 U.S. 313 (1971)