Post-Grant Review (PGR): Process, Grounds, and Strategy
Post-Grant Review is a trial proceeding before the Patent Trial and Appeal Board (PTAB) that allows any party to challenge the validity of a recently issued patent on any ground of invalidity recognized under Title 35 of the U.S. Code. Established by the America Invents Act (AIA) and codified at 35 U.S.C. §§ 321–329, PGR is one of the most powerful patent-challenge mechanisms in U.S. law, covering substantive grounds that narrower proceedings cannot reach. Understanding PGR's scope, timing constraints, and procedural architecture is essential for patent holders and challengers navigating the post-grant landscape.
Definition and scope
PGR applies exclusively to patents that issued from applications with an effective filing date on or after March 16, 2013 — the date the AIA's first-inventor-to-file provisions took effect (35 U.S.C. § 321). This limitation means PGR targets the generation of patents governed by the first-inventor-to-file system and does not apply to patents with pre-AIA effective filing dates.
The defining feature of PGR, relative to other post-grant proceedings, is the breadth of available invalidity grounds. A petitioner may raise any ground that could render a patent invalid, including:
- Lack of patentable subject matter under 35 U.S.C. § 101
- Anticipation (lack of novelty) under 35 U.S.C. § 102
- Obviousness under 35 U.S.C. § 103
- Inadequate written description, enablement, or definiteness under 35 U.S.C. § 112
This full-spectrum ground coverage distinguishes PGR from Inter Partes Review (IPR), which is limited to §§ 102 and 103 grounds based on patents or printed publications only.
A critical jurisdictional constraint governs filing timing: a PGR petition must be filed within 9 months of the challenged patent's grant or reissuance (35 U.S.C. § 321(c)). After that 9-month window closes, IPR becomes the primary inter partes challenge route if § 102/103 grounds apply.
How it works
PGR proceeds through a structured sequence of phases administered by PTAB under rules codified at 37 C.F.R. Part 42, Subpart C.
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Petition filing. The petitioner files a written petition identifying each challenged claim, the statutory grounds for each challenge, and supporting evidence. The petition must demonstrate that the challenge has a reasonable likelihood of prevailing on at least 1 of the challenged claims (35 U.S.C. § 324(a)). This threshold — "more likely than not" for at least 1 claim — is higher than the IPR institution standard.
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Patent owner preliminary response. The patent owner may file a preliminary response within 3 months of the petition being accorded a filing date. This response can introduce evidence under 37 C.F.R. § 42.207(c) to contest institution.
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Institution decision. PTAB issues an institution decision, either granting or denying the petition. If granted, the proceeding moves into the trial phase. PTAB may institute on all or a subset of the challenged claims.
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Discovery and trial. Once instituted, both parties may conduct limited discovery. The patent owner files a response, the petitioner may file a reply, and oral argument is typically held.
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Final written decision. PTAB must issue a final written decision within 12 months of the institution date (35 U.S.C. § 326(a)(11)), extendable by up to 6 months for good cause.
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Appeal. Either party may appeal the final written decision to the U.S. Court of Appeals for the Federal Circuit.
An estoppel provision under 35 U.S.C. § 325(e) bars a petitioner who receives a final written decision from raising in subsequent district court or ITC proceedings any ground that was raised or reasonably could have been raised during PGR. This estoppel risk is a central strategic consideration.
Common scenarios
PGR is most commonly deployed in three fact patterns:
Broad claim issuance after AIA prosecution. When a patent issues with claims that appear to sweep beyond what the prior art supports, a competitor that identifies § 101 or § 112 vulnerabilities — grounds unavailable in IPR — may file a PGR petition within the 9-month window to avoid prolonged district court litigation. This is particularly prevalent in software patent and biotechnology patent fields, where § 101 eligibility and enablement are frequently contested.
Defensive use by accused infringers. A party that receives a cease-and-desist letter or infringement complaint within the patent's first 9 months of grant can use PGR to challenge validity in a forum that statistically favors challengers at the institution stage, based on PTAB institution data published in the USPTO's Patent Trial and Appeal Board Statistics reports.
Portfolio clearing by market entrants. Companies entering a product market may audit AIA-generation patents held by incumbents and file PGR petitions against patents that appear vulnerable on § 112 grounds — particularly definiteness or lack of written description support — as part of a broader patent portfolio management or freedom-to-operate analysis.
Decision boundaries
The boundaries separating PGR from adjacent proceedings determine which mechanism applies in a given situation and carry significant strategic consequences. The comparison below captures the three principal inter partes or ex parte mechanisms:
| Criterion | PGR | IPR | Ex Parte Reexamination |
|---|---|---|---|
| Eligible patents | AIA (post-March 16, 2013 effective date) | All issued patents | All issued patents |
| Filing deadline | Within 9 months of grant | After 9 months of grant (or post-PGR) | No statutory deadline |
| Available grounds | Any invalidity ground (§§ 101, 102, 103, 112) | §§ 102 and 103 (prior art only) | § 102 and § 103 (prior art only) |
| Institution standard | More likely than not ≥ 1 claim is unpatentable | Reasonable likelihood ≥ 1 claim is unpatentable | Substantial new question of patentability |
| Petitioner participation | Active adversarial trial | Active adversarial trial | None after filing |
| Estoppel scope | Broad (raised or could have raised) | Broad (raised or could have raised) | None |
The threshold decision for any challenger is whether PGR's broader ground coverage justifies accepting the estoppel risk that attaches to a final written decision. A challenger confident in a § 101 or § 112 invalidity theory may prefer PGR precisely because those grounds cannot be brought in IPR. Conversely, a challenger with primarily prior-art-based arguments may elect to wait out the 9-month PGR window and file an IPR petition — preserving optionality and limiting estoppel exposure to § 102/103 grounds only.
Patent owners facing a PGR petition should assess whether patent prosecution history and claim amendments can rebut the petition's core arguments before the institution decision, since a strong preliminary response supported by expert declarations can defeat institution and avoid a full trial.
The broader regulatory framework governing PTAB proceedings, including procedural rules and fee structures, is addressed in the regulatory context for patent law. An overview of all major patent law topics is available on the site index.