Claim construction (Markman)
Claim construction is the process by which a court determines the meaning and scope of the patent claims. The Supreme Court held in Markman that this task belongs to the judge, not the jury, and the Federal Circuit refined the methodology en banc in Phillips. Teva later clarified the standard of review for the subsidiary factual findings that sometimes underlie a construction.
The rule
Claim construction is a matter of law for the court. In Markman v. Westview Instruments, Inc., 517 U.S. 370 (1996), the Supreme Court unanimously affirmed the Federal Circuit's en banc decision that interpretation of patent claims is reserved to the judge, both as a matter of historical practice and because uniformity of treatment within a patent counsels in favor of a single decisionmaker trained in the construction of written instruments.
The Federal Circuit's en banc decision in Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005), then resolved a long-running internal dispute about how that interpretive task should be performed. Phillips reaffirmed that claim terms are given the ordinary meaning they would have to a person of ordinary skill in the art at the time of the invention, read in the context of the entire patent, including the specification. The court rejected the heavily dictionary-driven approach of Texas Digital Systems, Inc. v. Telegenix, Inc., 308 F.3d 1193 (Fed. Cir. 2002), which had risked elevating abstract dictionary definitions over the inventor's actual usage in the patent.
Finally, Teva Pharmaceuticals USA, Inc. v. Sandoz, Inc., 574 U.S. 318 (2015), held that the ultimate question of claim construction remains a legal one, reviewed de novo, but that any subsidiary findings about extrinsic evidence are findings of fact reviewed for clear error under Federal Rule of Civil Procedure 52(a)(6).
Statutory and constitutional source
The need for claim construction arises from 35 U.S.C. § 112(b), which requires that a patent specification "conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the inventor or a joint inventor regards as the invention." Because infringement under 35 U.S.C. § 271 turns on whether an accused product or process falls within the metes and bounds of the claims, those metes and bounds must first be ascertained.
The Seventh Amendment did not require submission of claim construction to the jury. The Markman Court reviewed the historical record and concluded that, although infringement actions had long been tried to juries, the discrete question of patent-document interpretation had not been treated as a question for the jury at common law. Even if the historical evidence was equivocal, the Court reasoned, considerations of uniformity within a single patent and judicial competence in interpreting written instruments favored allocation to the court. See Markman, 517 U.S. at 388–91.
The framework the courts apply
Intrinsic evidence first
Under Phillips, claim construction proceeds from a hierarchy of evidence. Intrinsic evidence — the claims themselves, the specification, and the prosecution history — is the primary and usually dispositive source. The claims are read in light of the specification, which the Federal Circuit has called "the single best guide to the meaning of a disputed term." Phillips, 415 F.3d at 1315 (quoting Vitronics Corp. v. Conceptronic, Inc., 90 F.3d 1576, 1582 (Fed. Cir. 1996)).
The court begins with the claim language itself, including the use of the term in other claims in the same patent, which can illuminate the ordinary meaning. Differences between claims are presumed to reflect different scope under the doctrine of claim differentiation. The court then considers the specification: the patent's description, drawings, and any embodiments. The specification can define a term explicitly, can act as the inventor's lexicography, or can disclaim claim scope, but courts must be careful not to import limitations from particular embodiments into the claims absent a clear disavowal. See Phillips, 415 F.3d at 1320, 1323.
Prosecution history
The prosecution history — the public record of the patent's examination at the U.S. Patent and Trademark Office — is also intrinsic evidence. Statements made by the applicant to obtain the patent can narrow claim scope where the applicant clearly and unmistakably disclaimed coverage. See Omega Engineering, Inc. v. Raytek Corp., 334 F.3d 1314, 1324 (Fed. Cir. 2003). Prosecution disclaimer is closely related to, but doctrinally distinct from, prosecution history estoppel, which limits the reach of the doctrine of equivalents.
Statements made in related applications and in inter partes review proceedings before the Patent Trial and Appeal Board can also bear on claim meaning. See Aylus Networks, Inc. v. Apple Inc., 856 F.3d 1353 (Fed. Cir. 2017) (statements in IPR preliminary response can give rise to prosecution disclaimer).
Extrinsic evidence and dictionaries
Extrinsic evidence — including treatises, technical dictionaries, and expert testimony — is permissible but secondary. After Phillips, dictionaries may be consulted to understand the technical meaning of a term in the relevant field, but they cannot be used to override an inventor's contrary usage in the specification. The Federal Circuit characterized extrinsic evidence as generally less reliable than intrinsic evidence, both because it was not created in the context of the patent and because it may reflect the bias of the party introducing it. Phillips, 415 F.3d at 1318.
Expert testimony can be useful to explain the technology, the state of the art, or how a skilled artisan would understand the claim language, but expert testimony that conflicts with the intrinsic record is to be discounted.
Standard of review after Teva
Before Teva, the Federal Circuit reviewed claim construction entirely de novo under Cybor Corp. v. FAS Technologies, Inc., 138 F.3d 1448 (Fed. Cir. 1998) (en banc). Teva overruled Cybor in part. The ultimate construction remains a legal question reviewed without deference, but where a district court resolves a dispute about extrinsic evidence — for example, the meaning of a technical term to a person of ordinary skill at a given time — that subsidiary finding is reviewed for clear error. Teva, 574 U.S. at 331–33. When construction rests entirely on intrinsic evidence, review remains de novo.
How district courts conduct claim construction
Courts generally hold a Markman hearing at which the parties present their proposed constructions of disputed terms. Local patent rules in active patent districts — including the Eastern District of Texas, the Northern District of California, the District of Delaware, and the Western District of Texas — typically require an exchange of proposed terms for construction, exchange of proposed constructions with intrinsic and extrinsic support, and a joint claim construction statement before the hearing.
The hearing is generally non-evidentiary, but courts may take expert testimony where credibility determinations on extrinsic evidence are necessary. Following the hearing, the court issues a written claim construction order. Some courts construe a few dispositive terms; others address every disputed term identified by the parties. Most courts limit the number of terms the parties may submit.
Burden and proof
Because claim construction is a legal exercise rather than a factual contest, no party bears a traditional burden of proof on the meaning of a term. The party asserting a particular construction must persuade the court that its reading is correct under the Phillips framework. Where a subsidiary factual question turns on extrinsic evidence — typically expert testimony about how a skilled artisan would have understood a term — the proponent of the proposed factual finding must persuade the court by a preponderance of the evidence, and that finding is reviewed on appeal for clear error under Teva.
Means-plus-function claim limitations under 35 U.S.C. § 112(f) are construed under a distinct procedure. The court identifies the claimed function, then determines the corresponding structure disclosed in the specification. Failure to disclose corresponding structure renders the claim indefinite. See Williamson v. Citrix Online, LLC, 792 F.3d 1339 (Fed. Cir. 2015) (en banc in relevant part) (presumption against § 112(f) treatment for terms lacking the word "means" is not strong).
Interaction with related doctrines
Claim construction sits at the front of nearly every patent merits dispute. Once the court has fixed the scope of the claims, the construction governs the analysis of literal infringement and the doctrine of equivalents, the comparison of the claims to the prior art for anticipation under 35 U.S.C. § 102 and obviousness under § 103, and the assessment of written description and enablement under § 112(a). A construction adopted at the merits stage governs both validity and infringement. See Amazon.com, Inc. v. Barnesandnoble.com, Inc., 239 F.3d 1343, 1351 (Fed. Cir. 2001).
Claim construction also feeds into definiteness. Under Nautilus, Inc. v. Biosig Instruments, Inc., 572 U.S. 898 (2014), a claim is invalid if, read in light of the specification and prosecution history, it fails to inform a skilled artisan with reasonable certainty of the scope of the invention. Definiteness challenges are typically litigated together with claim construction.
In PTAB proceedings, the Board now applies the same Phillips standard as district courts. See 37 C.F.R. § 42.100(b) (2018 amendment). Before that amendment, the Board applied the broadest reasonable interpretation standard. The shift was intended to reduce inconsistent outcomes between district court and PTAB litigation involving the same patent. See inter partes review.
Practical notes
- The number of terms a party may submit for construction is typically capped by local rule or scheduling order. Selection should focus on terms whose construction is dispositive of infringement or validity.
- Disclaimers in the specification and prosecution history can be costly. Statements characterizing the invention or distinguishing prior art can be quoted back at trial and on appeal.
- Where a term has an established technical meaning, that meaning generally controls absent contrary indication in the patent. See Phillips, 415 F.3d at 1314.
- Construing a term to exclude a preferred embodiment is "rarely, if ever, correct." Vitronics, 90 F.3d at 1583. Courts are skeptical of constructions that read out embodiments described as part of the invention.
- Joint or dependent claims can be used to argue claim differentiation, but the doctrine is a presumption, not a rule, and yields to clear language in the specification or prosecution history.
- On appeal, parties should identify with precision whether the disputed issue rests on intrinsic evidence (de novo review) or on a finding about extrinsic evidence (clear-error review). The choice can be outcome-determinative.
Open questions
The boundary between findings of fact subject to clear-error review and ultimate conclusions of law subject to de novo review remains contested in the wake of Teva. Where intrinsic evidence is in tension with expert testimony, the Federal Circuit has often held that the intrinsic record controls and that any "factual" findings drawn from extrinsic evidence are immaterial, preserving de novo review in all but a narrow class of cases. See, e.g., Shire Development, LLC v. Watson Pharmaceuticals, Inc., 787 F.3d 1359 (Fed. Cir. 2015). The frequency with which Teva deference actually changes outcomes on appeal continues to be debated.
Other open questions include the proper treatment of statements in PTAB proceedings as prosecution disclaimer, the scope of disclaimer arising from arguments distinguishing prior art, and the effect of district court constructions on subsequent PTAB proceedings (and vice versa).
See also
- Markman v. Westview InstrumentsSupreme Court decision allocating claim construction to the judge.
- Phillips v. AWH Corp.Federal Circuit en banc framework for claim construction.
- Markman hearingsHow district courts conduct claim construction in practice.
- DefinitenessReasonable-certainty standard under Nautilus, often litigated alongside construction.
- Prosecution history estoppelDistinct doctrine that limits the reach of the doctrine of equivalents.
- Standards of reviewDe novo review with clear-error subfindings after Teva.
Last reviewed: 2026