Estoppel Arising from PTAB Trials

Inter partes review (IPR) and post-grant review (PGR) give challengers a faster, cheaper way to attack patent claims. The trade-off is estoppel. A petitioner that takes a challenge to a final written decision generally cannot try again on grounds it raised or could have raised.

Estoppel also reaches the petitioner’s real parties in interest and privies, so understanding its scope matters to anyone connected with a petition.

The statutory provisions

For IPR, 35 U.S.C. § 315(e) has two parts:

• § 315(e)(1), USPTO proceedings. The petitioner, its real party in interest or privy may not request or maintain a proceeding before the Office on any ground it raised or reasonably could have raised during the IPR.
• § 315(e)(2), civil actions and the ITC. The same parties may not assert in a district court action or an ITC investigation that a claim is invalid on any ground they raised or reasonably could have raised during the IPR.

For PGR, § 325(e) contains parallel provisions. Because PGR allows broader grounds, including §§ 101 and 112, PGR estoppel can potentially reach more kinds of invalidity arguments.

The trigger: a final written decision

Estoppel attaches claim by claim, and only for a claim that receives a final written decision. A petition that is denied institution does not create statutory estoppel. Nor does a proceeding terminated by settlement before a final written decision: under § 317, no § 315(e) estoppel attaches to the settling petitioner, its real parties in interest or privies on the basis of that petition.

“Raised or reasonably could have raised”

Early history: Shaw

When the Board could institute on some grounds and not others, the Federal Circuit read estoppel narrowly. In Shaw Industries Group, Inc. v. Automated Creel Systems, Inc. (Fed. Cir. 2016), the court held that grounds the Board declined to institute were not raised, and could not reasonably have been raised, “during” the IPR. Some later district courts applied that reasoning broadly. See the site’s discussion of Shaw Industries.

SAS ends partial institution

In SAS Institute Inc. v. Iancu (2018), the Supreme Court held that when the Board institutes an IPR, it must decide the patentability of all claims the petitioner challenged. The USPTO then stopped instituting on only some grounds. That removed the category of non-instituted grounds that Shaw had addressed. See PTAB guidance after SAS.

Caltech v. Broadcom: the current rule

In California Institute of Technology v. Broadcom Ltd. (Fed. Cir. 2022), the Federal Circuit held that estoppel applies not only to grounds actually included in the petition, but to all claims and grounds not in the IPR that reasonably could have been included in the petition. The court overruled Shaw to the extent it suggested otherwise.

Many district courts ask whether a skilled searcher conducting a diligent search reasonably could have been expected to find the art. Under that approach, patents and printed publications the petitioner knew of, or would have found through a reasonable search, are generally within the estoppel.

What estoppel does not reach

Prior-art products and systems

IPR grounds are limited to anticipation and obviousness based on patents and printed publications (§ 311(b)). Estoppel follows that limit. A recurring question in district court is whether a defendant can rely on a prior-art product or system, rather than a document, after losing an IPR.

In Ingenico Inc. v. IOENGINE, LLC (Fed. Cir. 2025), the Federal Circuit held that IPR estoppel does not bar a defendant from relying on prior-art systems or products in court, even if they share disclosures with printed publications that could have been raised in the IPR.

Other grounds and proceedings

• Other statutory grounds. IPR estoppel does not reach §§ 101 or 112 defenses, which cannot be raised in an IPR.
• Ex parte reexamination. A request for ex parte reexamination, by itself, carries no estoppel for the requester. (A petitioner already estopped by an IPR decision may, however, be barred from requesting reexamination on the same grounds under § 315(e)(1).)

Comparing the estoppel provisions

	IPR	PGR	Ex parte reexam
Statute	§ 315(e)	§ 325(e)	None
Trigger	Final written decision	Final written decision	Not applicable
Parties bound	Petitioner, RPIs, privies	Petitioner, RPIs, privies	Not applicable
Grounds	§§ 102/103 on patents and printed publications	Broader, including §§ 101 and 112	Not applicable
Settled before decision	No estoppel (§ 317)	No estoppel (§ 327)	Not applicable

Key takeaways

• IPR estoppel (§ 315(e)) and PGR estoppel (§ 325(e)) attach only after a final written decision.
• The estoppel covers grounds the petitioner raised or reasonably could have raised, and binds RPIs and privies.
• Caltech v. Broadcom (Fed. Cir. 2022) extends estoppel to grounds that reasonably could have been included in the petition, overruling Shaw to that extent.
• IPR estoppel is limited to patents and printed publications; prior-art products and systems generally remain available in court.
• Settlement before a final written decision avoids estoppel for the settling petitioner under § 317.