What Is an Inter Partes Review (IPR)?

An inter partes review — commonly called an IPR — is a proceeding before the US Patent Trial and Appeal Board (PTAB) in which a third party challenges the validity of a granted patent. It is the most frequently used mechanism for attacking US patents outside of federal court litigation, and it has fundamentally changed the balance of power between patent holders and accused infringers since its introduction in 2012.

In plain terms: if someone believes your patent should not have been granted — because the invention was not novel or was obvious in light of prior art — they can petition the PTAB to review and potentially cancel your patent claims. The process is faster and cheaper than challenging a patent in court.

How an IPR Works

Who can file: Any person or entity other than the patent owner, provided they have not already been served with an infringement complaint more than one year earlier.

Grounds for challenge: IPR is limited to novelty and obviousness challenges based on prior art patents and printed publications. Other invalidity grounds — such as enablement, written description, or patent-eligible subject matter — cannot be raised in an IPR.

Petition: The challenger files a detailed petition explaining why each challenged claim is unpatentable, supported by prior art references and often accompanied by expert declarations. As of the January 2025 USPTO fee schedule, the IPR request fee is $23,750 (plus a $28,125 post-institution fee if the petition is granted).

Institution decision: The PTAB decides whether to "institute" the IPR — that is, whether there is a reasonable likelihood that the petitioner would prevail on at least one challenged claim. Approximately 60–65% of petitions are instituted.

Trial: If instituted, a full adversarial trial takes place before a panel of three PTAB judges. Both sides submit evidence, expert testimony, and legal arguments. Oral hearings are held. The entire process from institution to final written decision takes 12 months (extendable to 18 months in complex cases).

Final written decision: The PTAB issues a decision on whether each challenged claim is unpatentable. Claims found unpatentable are cancelled — permanently. There is no damages award, injunction, or monetary relief. The IPR determines only whether the claims survive.

Appeal: Either party can appeal the PTAB's decision to the US Court of Appeals for the Federal Circuit.

Why IPR Matters for Inventors

IPR has become the preferred tool for companies accused of patent infringement to challenge the validity of the asserted patent — often filed within days of receiving a cease-and-desist letter or infringement complaint. The statistics are sobering for patent holders: of claims that reach a final written decision, approximately 60–70% are found unpatentable.

This means that sending a cease-and-desist letter to a well-resourced company carries a real risk that the recipient will respond not with a licensing negotiation but with an IPR petition aimed at invalidating your patent. Before asserting your patent, consider whether your claims would survive the scrutiny of an IPR proceeding.

IPR vs District Court Litigation

The lower standard of proof in IPR — preponderance of evidence versus clear and convincing evidence in court — is one of the key reasons patents are more vulnerable at the PTAB than in litigation.

Equivalents Outside the US

Other jurisdictions have post-grant challenge mechanisms, though none are identical to the US IPR:

EPO Opposition: Any third party can file an opposition within 9 months of grant. Broader grounds than IPR — includes added subject matter, insufficiency, and non-patentable subject matter. The opposition division (three examiners) decides. The rate of patent revocation or amendment in EPO oppositions is high.

China (CNIPA Invalidation): Any party can request invalidation of a Chinese patent at any time after grant. The Patent Re-examination Board (PRB) reviews the request. Both utility patents and utility models can be challenged.

Japan (JPO Trial for Invalidation): Any interested party can file a trial for invalidation before the JPO's Trial and Appeal Department. The standard of proof is similar to the US IPR standard.

Sources

1. 35 U.S.C. § 311–319 — Inter Partes Review — Complete US statutory framework for IPR proceedings
2. USPTO PTAB — Patent Trial and Appeal Board conducting IPR proceedings
3. EPC Article 99–105 — Opposition — European equivalent post-grant opposition procedure
4. CNIPA Patent Invalidation — Chinese patent invalidation proceedings at the Patent Re-examination Board
5. JPO Trial for Invalidation — Japanese patent invalidation proceedings