What is interference estoppel in patent law?

Interference estoppel in patent law refers to the principle that prevents a party from re-litigating an issue they lost in a previous interference proceeding. As stated in MPEP 2308.03: “If a party loses on an issue, it may not re-litigate the issue before the examiner or in a subsequent Board proceeding.” There are two main types of interference estoppel:

  • Estoppel on the merits: A losing party is barred from seeking a claim that would have been anticipated or rendered obvious by the subject matter of the lost count.
  • Procedural estoppel: A losing party is barred from seeking relief from the examiner that could have been—but was not—sought in the interference.

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Topics: MPEP 2300 - Interference And Derivation Proceedings, MPEP 2308.03 - Estoppel Within The Office, Patent Law, Patent Procedure
Tags: Interference Estoppel, MPEP, patent law, USPTO