What is procedural estoppel in patent interference 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.

Procedural estoppel in patent interference proceedings prevents a losing party from seeking relief that could have been—but was not—sought during the interference. MPEP 2308.03 states:

“A losing party is procedurally barred from seeking from the examiner relief that could have been–but was not–sought in the interference.”

This means that if an applicant had the opportunity to make an argument or amendment during the interference but failed to do so, they cannot later make that argument or amendment in subsequent proceedings. For example, if an applicant could have moved to amend a claim during the interference but did not, they cannot later amend that claim in a continuing application to overcome the grounds for unpatentability established in the interference.