Inter Partes Review (IPR)

35 U.S.C. §§ 311–319

Statutory basis (AIA 2011)

§ 102 / § 103 only

Grounds (prior art only, not § 101 or § 112)

1 year

Filing deadline from service of complaint

Preponderance

Burden of proof (vs. clear-and-convincing in court)

~60–70%

Institution rate of filed petitions

~50–65%

Instituted claims cancelled at trial

12 months

Maximum trial length from institution

§ 315(e)

Estoppel statute — binds petitioner at final written decision

What is the standard of proof in an IPR vs district court patent litigation?

In an inter partes review (IPR), the petitioner must show unpatentability by a preponderance of the evidence — more likely than not (>50%) that the challenged claims are invalid. This is a significantly lower burden than the clear-and-convincing evidence standard required to prove invalidity in US district court litigation. This lower standard, combined with PTAB's technical expertise (three-judge administrative patent judges per panel), is one reason IPR is so effective at invalidating patents — PTAB regularly finds claims unpatentable that survived years of district court challenges. The institutional decision (whether to proceed with trial) uses an even lower 'reasonable likelihood' standard (§ 314(a)).

What is IPR estoppel and how does it affect later district court litigation?

IPR estoppel under 35 U.S.C. § 315(e) prevents an IPR petitioner from asserting in a later district court or ITC proceeding that a patent claim is invalid on any ground that was raised or reasonably could have been raised during the IPR. This means: if the IPR fails to cancel a claim, the petitioner cannot re-litigate the same prior art arguments in district court. Estoppel attaches when the PTAB issues a final written decision — if the petitioner settles before a final written decision, no estoppel applies. The scope of 'reasonably could have been raised' is contested: courts have generally interpreted it broadly for prior-art-based invalidity grounds. Estoppel does not apply to grounds based on prior commercial use, prior public knowledge, or § 112 (specification) defects — these can still be raised in district court even after an IPR final written decision.

Can you settle an IPR? What happens when you do?

Yes, IPR proceedings can be settled. Under 35 U.S.C. § 317, the parties may file a joint request to terminate the proceeding and submit the settlement agreement. PTAB will typically grant termination if: (a) no claim of the patent has been cancelled, (b) the settlement agreement is filed, and (c) the motion for joinder (if any) has been dealt with. Key strategic considerations: (1) Estoppel only attaches at final written decision — settling before that avoids estoppel, preserving the petitioner's right to raise the same prior art in district court. (2) PTAB may continue the proceeding even after settlement if it has already expended substantial resources or if the public interest warrants it (rare). (3) Settlement agreements must be filed with the USPTO and become part of the file wrapper, but parties can request that they be kept confidential under § 317(b). A settlement often includes a patent license, a covenant not to sue, or a business deal as part of the resolution.

What are the differences between IPR, PGR, and ex parte reexamination?

Inter Partes Review (IPR): available after the 9-month PGR window (or if no PGR filed), only on § 102/103 grounds using prior-art patents and printed publications. 1-year filing deadline from service of complaint. Petitioner participates actively in trial. Full estoppel on final written decision. Post-Grant Review (PGR): available within 9 months of patent grant or reissuance. Broader grounds — any ground that could render the patent invalid, including § 101, § 112, prior commercial use, prior public knowledge. Higher institution threshold: 'more likely than not' that at least one claim is unpatentable (vs. 'reasonable likelihood' for IPR). Full estoppel. Generally more powerful than IPR but short filing window. Ex parte reexamination: any person can anonymously request reexamination based on prior-art patents or printed publications. Low threshold ('substantial new question of patentability'). USPTO examines the patent again — the requestor has very limited participation rights after the request is granted. No estoppel. Can be filed at any time. Slower than IPR (18–36 months). Often less effective for petitioners because the patent owner controls the prosecution.

What percentage of IPR petitions succeed at PTAB?

PTAB institution rates and outcomes have changed significantly since IPR was introduced in 2012. As of 2023–2024, roughly 60–70% of IPR petitions that are filed are instituted (PTAB agrees to proceed to trial). Of the claims that go through a full IPR trial, roughly 50–65% are ultimately cancelled or found unpatentable (either all, some, or with amended claims). Overall, when accounting for settlements, voluntary dismissals, and cases where institution is denied, roughly 35–45% of all petitioned claims end up cancelled. Institution rates have been affected by the Fintiv rules (PTAB may decline to institute if parallel district court litigation is too advanced) and by NHK/Fintiv guidance that gives PTAB discretion to deny institution for efficiency reasons. Petitioners can improve their odds by filing high-quality petitions with strong claim charts, compelling expert declarations, and explicit mapping of every claim limitation to prior-art disclosures.