StacksVerified U.S. regulatory reference

37 CFR §42.201

Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗
A person who is not the owner of a patent may file with the Office a petition to institute a post-grant review of the patent unless:
  1. (a)Before the date on which the petition for review is filed, the petitioner or real party-in-interest filed a civil action challenging the validity of a claim of the patent; or
  2. (b)The petitioner, the petitioner's real party-in-interest, or a privy of the petitioner is estopped from challenging the claims on the grounds identified in the petition.