Literal infringement
Literal infringement is the simplest theory of patent infringement: every limitation of a properly construed claim must be found, exactly, in the accused product or process. The analysis is mechanical once the claim has been construed. Anything less than complete identity of every limitation — and the patentee must turn to the doctrine of equivalents or recover nothing.
The rule
Under 35 U.S.C. § 271(a), whoever without authority makes, uses, offers to sell, sells, or imports any patented invention within the United States during the term of the patent infringes the patent. Literal infringement occurs when a properly construed claim reads on the accused product or process, limitation by limitation, exactly. The Federal Circuit has stated the rule in a single sentence: "To establish literal infringement, every limitation set forth in a claim must be found in an accused product, exactly." Southwall Technologies, Inc. v. Cardinal IG Co., 54 F.3d 1570, 1575 (Fed. Cir. 1995).
The "every-element" rule — sometimes called the "all-elements" rule — is foundational. The Supreme Court reiterated in Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17, 29 (1997), that "[e]ach element contained in a patent claim is deemed material to defining the scope of the patented invention." A single missing limitation defeats literal infringement, regardless of how closely the accused product otherwise resembles the patented invention.
Statutory and constitutional source
The statutory basis is 35 U.S.C. § 271(a):
Except as otherwise provided in this title, whoever without authority makes, uses, offers to sell, or sells any patented invention, within the United States, or imports into the United States any patented invention during the term of the patent therefor, infringes the patent.
Section 271(a) creates a strict-liability regime. Intent and knowledge are not elements of direct infringement. See Global-Tech Appliances, Inc. v. SEB S.A., 563 U.S. 754, 761 n.2 (2011) (noting that direct infringement is a strict-liability offense). The Patent and Copyright Clause, U.S. Const. art. I, § 8, cl. 8, supplies the constitutional foundation for the patent right itself.
The framework the courts apply
Two-step analysis
Patent infringement analysis proceeds in two steps. First, the court construes the claims as a matter of law under claim construction doctrine. Second, the trier of fact compares the properly construed claims to the accused device or process to determine whether every limitation is present. The Federal Circuit articulated this two-step approach in Markman v. Westview Instruments, Inc., 52 F.3d 967, 976 (Fed. Cir. 1995) (en banc), aff'd, 517 U.S. 370 (1996), and reaffirmed it in Cybor Corp. v. FAS Technologies, Inc., 138 F.3d 1448, 1454 (Fed. Cir. 1998) (en banc).
The first step is a question of law, reviewed de novo on appeal except as to subsidiary findings of fact about extrinsic evidence, which are reviewed for clear error. See Teva Pharmaceuticals USA, Inc. v. Sandoz, Inc., 574 U.S. 318 (2015). The second step is a question of fact, reviewed for substantial evidence after a jury verdict and for clear error after a bench trial.
Comparing the construed claim to the accused product
The comparison is between the construed claim and the accused product or process — not between the patented commercial embodiment and the accused product. See Zenith Laboratories, Inc. v. Bristol-Myers Squibb Co., 19 F.3d 1418, 1423 (Fed. Cir. 1994). It is a frequent error to compare two competing products; the proper comparison is claim-to-product.
The accused product must include every limitation of the asserted claim. If the claim recites elements A, B, C, and D, the accused product must contain each of A, B, C, and D, performing the function and meeting the structural requirements set out in the construed claim. The presence of additional elements in the accused product is irrelevant to literal infringement of an open ("comprising") claim. See Mannesmann Demag Corp. v. Engineered Metal Products Co., 793 F.2d 1279, 1282 (Fed. Cir. 1986).
Open, closed, and partially closed claim language
Claim transitional phrases bear directly on literal infringement analysis. "Comprising" is open: the claim covers products that contain the listed elements together with additional, unrecited elements. "Consisting of" is closed: the claim is limited to the listed elements and excludes any unrecited element. "Consisting essentially of" is partially closed: it covers products containing the listed elements together with unrecited elements that do not materially affect the basic and novel characteristics of the invention. See AK Steel Corp. v. Sollac & Ugine, 344 F.3d 1234, 1239 (Fed. Cir. 2003).
Apparatus claims
For an apparatus claim, the accused product infringes if it possesses every claimed structural element, regardless of whether the product is actually used in an infringing manner. The capability to perform a recited function is generally enough where the claim is drafted in terms of structure capable of performing a function. See Hewlett-Packard Co. v. Bausch & Lomb Inc., 909 F.2d 1464, 1468 (Fed. Cir. 1990). Means-plus-function limitations under 35 U.S.C. § 112(f) are a partial exception: they require either the disclosed structure or its statutory equivalent.
Method claims
A method claim is infringed only when each step of the method is performed. The mere sale of an apparatus capable of practicing a method does not literally infringe the method claim — the steps must be carried out. See Joy Technologies, Inc. v. Flakt, Inc., 6 F.3d 770, 775 (Fed. Cir. 1993). Method claims also raise divided infringement questions where multiple actors perform different steps; that issue is governed by Akamai Technologies, Inc. v. Limelight Networks, Inc., 797 F.3d 1020 (Fed. Cir. 2015) (en banc).
Section 271(a) acts
Section 271(a) enumerates five infringing acts: making, using, offering to sell, selling, and importing. Each is independently sufficient. "Making" includes assembly of the patented invention; "using" includes employing the invention for its intended purpose. See NTP, Inc. v. Research in Motion, Ltd., 418 F.3d 1282 (Fed. Cir. 2005) (use of a system claim occurs where control is exercised and beneficial use obtained). "Offering to sell" was added to § 271(a) in 1996 to implement TRIPS obligations and reaches commercial offers under contract-law principles. See Rotec Industries, Inc. v. Mitsubishi Corp., 215 F.3d 1246, 1257 (Fed. Cir. 2000). The conduct must occur within the United States or, for importation, involve crossing the U.S. border.
Burden and proof
The patentee bears the burden of proving infringement by a preponderance of the evidence. See SmithKline Diagnostics, Inc. v. Helena Laboratories Corp., 859 F.2d 878, 889 (Fed. Cir. 1988). Infringement is a question of fact. Where the issue is tried to a jury, the verdict is reviewed for substantial evidence; where to the bench, the court's findings are reviewed for clear error.
Proof generally requires comparing the accused product element-by-element to each limitation of the construed claim. Most patentees use a claim chart at trial that pairs each claim limitation with the corresponding feature of the accused product, supported by source code, schematics, technical documentation, and expert testimony. Conclusory expert opinion that does not address each limitation is insufficient. See Network Commerce, Inc. v. Microsoft Corp., 422 F.3d 1353, 1363 (Fed. Cir. 2005).
Interaction with related doctrines
Literal infringement is the floor of the infringement inquiry. If literal infringement fails because one or more limitations are not literally present, the patentee may pursue infringement under the doctrine of equivalents, subject to the limits imposed by prosecution history estoppel, the all-elements rule, the disclosure-dedication rule, and claim vitiation. Both theories share the same construed claim as their starting point, so an erroneous construction is reversible regardless of theory.
Literal infringement also interacts with indirect infringement. Indirect infringement under 35 U.S.C. § 271(b) and (c) requires an underlying act of direct infringement. See Limelight Networks, Inc. v. Akamai Technologies, Inc., 572 U.S. 915, 921 (2014). The direct act may be literal or by equivalents, but it must occur. A defendant who induces a third party cannot be held liable for inducement absent proof that the third party directly infringed.
An accused infringer can defeat infringement by showing that the asserted claim is invalid or unenforceable. Validity defenses turn on doctrines such as anticipation, obviousness, written description and enablement, definiteness, and the subject-matter eligibility requirement of § 101. Invalidity must be proved by clear and convincing evidence. See Microsoft Corp. v. i4i Limited Partnership, 564 U.S. 91 (2011).
The exhaustion doctrine can also defeat literal infringement: an authorized first sale of a patented article exhausts the patentee's rights with respect to that article. See Impression Products, Inc. v. Lexmark International, Inc., 581 U.S. 360 (2017).
Practical notes
- Claim construction usually decides the case. Most literal-infringement disputes turn on what a claim term means rather than on whether the accused product has a particular feature.
- Element-by-element claim charts are essential. Failure to address each limitation creates a directed-verdict risk.
- Apparatus claims directed at "capability" rather than active use raise difficult questions about how much functional support is required. Software claims are particularly sensitive to this distinction.
- The accused product is what infringes — not the alleged infringer's marketing materials, although those materials may be evidence of infringement.
- Indirect-infringement allegations should not skip the direct-infringement element. A jury must find direct infringement before reaching inducement or contributory infringement.
- Method-claim cases require proof that each step actually occurred, often requiring discovery into customer or end-user conduct.
- Geographic limits matter. § 271(a) reaches only conduct in the United States; offshore conduct is reached, if at all, only through 35 U.S.C. § 271(f) or § 271(g).
Open questions
The reach of § 271(a) over distributed computing systems remains imperfectly settled. NTP v. Research in Motion located use of a transnational system at the place of control, but later cases have grappled with cloud-based architectures where servers, users, and data flows span borders. The Federal Circuit's case law on situs of use continues to evolve.
Software products that lock or unlock features by license key raise unsettled questions about whether possession of code that is capable, but not currently configured, to perform a claimed function constitutes literal infringement. Courts have reached different results depending on how the claim is drafted and whether the accused product, as shipped, possesses the claimed capability without modification.
See also
- Claim constructionFirst step of every infringement analysis.
- Doctrine of equivalentsBackup theory when literal infringement fails.
- Direct infringementStatutory framework under § 271(a).
- Indirect infringementInducement and contributory infringement under § 271(b)–(c).
- Patent exhaustionFirst-sale defense to infringement.
- Markman v. WestviewOrigin of the two-step framework.
Last reviewed: 2026