Is res judicata applicable in patent reexamination proceedings?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

No, res judicata (claim preclusion) is generally not applicable in patent reexamination proceedings. MPEP § 2659 states:

“The doctrine of res judicata based on a court holding in an infringement proceeding is not applicable in reexamination proceedings, because the Office was not a party to the litigation.”

This means that even if a court has made a decision in an infringement case, the USPTO is not bound by that decision in a reexamination proceeding because it was not involved in the original litigation.