IPR vs District Court: Where Should You Challenge a Patent?

The Situation

A company accused of patent infringement, or one that expects to be, usually has two main venues for attacking the validity of the patent: inter partes review before the Patent Trial and Appeal Board, and an invalidity defense or counterclaim in federal district court. The two are not mutually exclusive, and many defendants pursue both. The choice turns on the grounds available, the evidence required, and the timing of the dispute.

How Inter Partes Review Works

Inter partes review is a trial proceeding at the USPTO. Under 35 U.S.C. § 311(b), a petitioner may challenge claims only under § 102 or § 103, and only on the basis of prior art consisting of patents and printed publications. The petition must set out each ground and the supporting evidence, usually with an expert declaration.

The patent owner may file a preliminary response, and the Board decides whether to institute review roughly six months after the petition is filed. If review is instituted, the statute requires a final written decision within one year of institution, extendable by up to six months for good cause. Either party may appeal to the Federal Circuit.

Three features make inter partes review attractive to challengers:

• Lower burden: Unpatentability need only be shown by a preponderance of the evidence, compared with the clear and convincing standard that applies in court under Microsoft Corp. v. i4i Ltd. Partnership (2011)
• Technical decision makers: Administrative patent judges have technical backgrounds and are accustomed to reading prior art and patent claims
• Speed and cost: The statutory schedule produces a decision far sooner than most district court trials

Since November 2018 the Board has applied the same Phillips standard of claim construction used in district court, so a construction adopted in one forum carries weight in the other.

Limits of Inter Partes Review

The statute imposes a firm deadline. Under 35 U.S.C. § 315(b), a petition is barred if it is filed more than one year after the petitioner, its real party in interest, or a privy is served with a complaint alleging infringement of the patent. Defendants who intend to petition need to have their prior art search well under way early in the case.

Institution is also discretionary. The USPTO's approach to discretionary denial changed significantly in 2025, including Director-level involvement in institution decisions and renewed weight on factors such as the status of parallel litigation. Historical institution rates are a poor guide to current practice, and petitioners should review the Director's current guidance before planning around an instituted review.

Finally, estoppel under § 315(e) attaches once a final written decision issues. The petitioner may not later assert in court or at the USPTO any ground that it raised or reasonably could have raised during the review. A petitioner that loses at the Board therefore gives up most of its patent and publication art for trial.

What District Court Offers

District court is the only forum that can resolve the whole dispute. The court decides infringement, validity, and remedies together, and a jury typically decides the factual questions. The defendant can raise every invalidity theory, including subject matter eligibility under § 101, written description, enablement, and indefiniteness under § 112, and prior public use or sale under the on-sale bar, which inter partes review cannot address.

The cost is a higher burden of proof and a longer schedule. Because an issued patent is presumed valid, the challenger must prove invalidity by clear and convincing evidence, and a lay jury may be less receptive to a technical obviousness argument than an expert panel.

Ex Parte Reexamination

A third option is ex parte reexamination, in which anyone may ask the USPTO to reconsider a patent on the basis of patents and printed publications that raise a substantial new question of patentability. It carries no one-year time bar and no estoppel of the kind that follows inter partes review, and it is inexpensive to request. The requester, however, does not participate after the request is granted, so the patent owner and the examiner shape the outcome.

Choosing a Forum

Consider inter partes review when the best invalidity case is a strong combination of printed references, the deadline under § 315(b) can be met, and a stay of the litigation pending review would help. Rely on district court when the best arguments are eligibility, § 112, or on-sale activity, or when you prefer not to risk estoppel on your prior art. Many defendants file a petition on their strongest printed art and preserve other theories for trial.

Preparing the Record

Both forums reward early, thorough work on the prior art and on the patent owner's litigation history. ArcPrime's patent invalidation tools help teams assemble prior art and claim-by-claim analysis for either venue.