What IPR is and why it was created
Inter partes review (IPR) is a patent trial proceeding created by the America Invents Act (AIA) and conducted by the Patent Trial and Appeal Board (PTAB). It was established to provide a faster, cheaper alternative to district court litigation for challenging patent validity on prior art grounds. Before IPR, patent validity was primarily challenged in district court (expensive, slow) or through inter partes reexamination at the USPTO (cheaper but one-sided, no oral argument, no discovery). IPR improved on both by: providing a quasi-adversarial trial proceeding; having specialized patent judges (administrative patent judges) decide the issues; completing the proceeding within 12 months of institution; allowing limited discovery; and reaching decisions at a preponderance of evidence standard (lower than the clear and convincing standard in district court). Since its inception in September 2012, over 10,000 IPR petitions have been filed.
Grounds for IPR: prior art only
IPR can only be requested on grounds of prior art under 35 U.S.C. §§ 102 (anticipation) and 103 (obviousness). The only prior art that can be used: patents and printed publications. IPR cannot be used to challenge claims based on: § 101 subject matter eligibility (Alice/Mayo); § 112 written description, enablement, or definiteness; public use or on-sale bar (§ 102(b)); prior inventor defenses; or any other invalidity ground outside §§ 102/103 based on patents and printed publications. This scope limitation is significant — § 101 challenges and § 112 challenges must be raised in district court. For NPE-asserted software patents with § 101 vulnerabilities, petitioners sometimes pursue IPR on § 103 grounds while also moving to dismiss on § 101 grounds in district court simultaneously.
Filing an IPR petition
An IPR petition must be filed with PTAB and include: the identity of the petitioner and any real parties in interest; the grounds of challenge (which prior art, applied to which claims, under § 102 or § 103); a copy of each prior art patent or publication; a claim chart mapping each prior art reference to each challenged claim element; a declaration from a qualified technical expert supporting the petition's analysis; and the patent to be challenged. The petition fee is $17,500 for up to 20 claims (large entity) plus $250 per additional claim. The petition is limited to 14,000 words (about 60 pages). Quality of the petition is paramount — PTAB decides whether to institute based solely on the petition and the patent; a poorly drafted petition is unlikely to be instituted. Practitioners typically spend $50,000–$150,000 on preparing a strong IPR petition with expert support.
Estoppel: the major risk of IPR
The most significant strategic risk of IPR is estoppel. Under 35 U.S.C. § 315(e), if IPR is instituted and a final written decision is entered, the petitioner (and any real party in interest or privy) is estopped from asserting in district court, ITC, or PTAB any ground of invalidity that was raised or reasonably could have been raised during the IPR. 'Reasonably could have been raised' is broad — it includes prior art that a diligent searcher would have found and that could have been used in the IPR. This means that after an IPR final written decision, the petitioner loses most of its prior art invalidity defenses in district court. If the IPR fails to cancel all challenged claims, the petitioner may be stuck with a narrowed invalidity defense. Strategic implication: before filing an IPR petition, petitioners should ensure they have found the best available prior art and that they are confident in the case — filing a weak petition and losing can be worse than not filing at all.
Patent owner strategies in IPR
Patent owners facing IPR petitions have several response options. Pre-institution: the patent owner may file a preliminary response within 3 months of institution, presenting arguments against institution; this can be effective if the petition has threshold deficiencies, prior art is weak, or discretionary denial doctrines (like Fintiv) apply. During trial: the patent owner can file a motion to amend claims — proposing substitute claims that are narrowed to avoid the prior art; PTAB grants motions to amend in only about 10–20% of cases, but a successful amendment can preserve some claim scope; after the Aqua Products decision (Fed. Cir. 2017), the petitioner bears the burden of showing that substitute claims are unpatentable, not the patent owner. Appeal: PTAB final written decisions can be appealed to the Federal Circuit; the Federal Circuit reviews PTAB's legal conclusions de novo and factual findings for substantial evidence; the Federal Circuit reversal rate of PTAB final written decisions is approximately 10–15%.
IPR vs. district court invalidity
The choice between challenging a patent through IPR or district court invalidity requires careful analysis. IPR advantages: faster (12 months vs. 2–5 years in district court); cheaper (less expensive than district court litigation overall); lower standard of proof (preponderance vs. clear and convincing); specialized judges (administrative patent judges have technical expertise); no jury. District court advantages: broader grounds (§ 101, § 112, § 102(b) on-sale/public use, all prior art types); injunctive relief available; countersuit with affirmative damages claims; no estoppel risk if IPR not filed. Many defendants in patent suits pursue both: file an IPR petition on the best prior art grounds, and challenge § 101 and § 112 in district court. The risk of estoppel from a failed IPR means petitioners should choose their IPR prior art carefully — reserve other prior art for district court and file IPR only on the strongest §§ 102/103 grounds based on patents and printed publications.
Frequently Asked Questions
What is inter partes review (IPR)?
Inter partes review (IPR) is a post-grant trial proceeding at the Patent Trial and Appeal Board (PTAB) that allows any third party to challenge the validity of claims in an issued US patent based on prior art (patents and printed publications under 35 U.S.C. §§ 102 and 103). IPR was created by the America Invents Act (AIA) and became effective September 16, 2012, replacing the prior inter partes reexamination proceeding. IPR can only be initiated after the patent has been in force for 9 months (or after any post-grant review period has ended). The petitioner must show a 'reasonable likelihood that the petitioner would prevail with respect to at least 1 of the claims challenged.' If instituted, the trial is conducted before a three-judge panel of PTAB administrative patent judges and must conclude within one year. The standard of proof at PTAB is preponderance of the evidence (more likely than not), lower than the clear and convincing evidence standard required in district court invalidity challenges.
Who can file an IPR petition?
Anyone who is not the patent owner can file an IPR petition, with two important restrictions: (1) Time bar — a petition cannot be filed more than one year after the petitioner (or a real party in interest or privy of the petitioner) was served with a complaint for patent infringement (35 U.S.C. § 315(b)); (2) Estoppel — if a petitioner files an IPR petition, they are estopped from raising in district court, ITC, or PTAB any ground of invalidity that was raised or reasonably could have been raised during the IPR. The one-year time bar is strictly enforced — even if the case was later dismissed. Multiple petitioners can file IPR petitions against the same patent, though PTAB may consolidate them or use one as the primary petition. A party that is in privity with an entity that previously filed a petition (e.g., an indemnitor) may also be time-barred by the prior petition.
What is the IPR institution threshold?
PTAB institutes an IPR trial only if the petition demonstrates a 'reasonable likelihood that the petitioner would prevail with respect to at least 1 of the claims challenged' (35 U.S.C. § 314(a)). This is a petition-stage threshold — it does not mean the claims are actually invalid, only that there is a reasonable likelihood of invalidity. PTAB has discretion to deny institution even if the threshold is met. The Supreme Court in Thryv v. Click-to-Call (2020) held that PTAB's decision whether to institute is final and non-appealable. Important discretionary denial doctrines: (1) Apple v. Fintiv (PTAB 2020) — PTAB may deny institution when parallel district court litigation is advanced and trial is near; (2) General Plastic factors — PTAB may deny a follow-on petition against the same patent on the same art if PTAB already considered and denied an earlier petition. After the NHK-Fintiv doctrines were established, institution rates declined; the USPTO issued guidance in 2022 partially limiting Fintiv considerations.
What happens during an IPR trial?
After institution, an IPR trial follows a structured schedule: (1) Institution decision: PTAB institutes on some or all challenged claims; the patent owner has 3 months to file a Patent Owner Response; (2) Patent Owner Response: the patent owner defends the claims with arguments and evidence; the patent owner may also submit expert testimony; (3) Petitioner Reply: the petitioner has 1 month to reply; (4) Oral argument: held at the USPTO; both sides argue the case before a three-judge panel for 30–60 minutes (no new evidence, just argument); (5) Final Written Decision: PTAB must issue its decision within 1 year of institution; the decision addresses each challenged claim's validity under the instituted grounds. PTAB can also allow the patent owner to move to amend claims during the trial — a rarely-successful but important option. The entire trial must conclude within 1 year of institution (12 months), extendable to 18 months for good cause. Note: claim construction at PTAB since November 2018 uses the Phillips standard (same as district court), not the broadest reasonable interpretation.
What are the IPR statistics on invalidity rates?
IPR has proven highly effective at invalidating patent claims. Key PTAB statistics (cumulative through recent years): Institution rate: approximately 60–65% of filed petitions are instituted; of those instituted, approximately 70–80% result in all challenged claims being canceled or some claims being canceled. Overall, roughly 40–50% of all challenged claims are ultimately canceled. Among the most commonly challenged patents are those asserted by non-practicing entities (NPEs or 'patent trolls') — software patents, business method patents, and broad functional claims are particularly vulnerable. Petitioners with strong prior art and well-drafted petitions with expert declarations have higher success rates. After the Unified Patents v. Realtime Data case, institutional petitioners (like Unified Patents, which files petitions on behalf of members in specific technology areas) have filed many petitions against NPE-asserted patents.