Direct infringement under 35 U.S.C. § 271(a) reaches anyone who makes, uses, offers to sell, sells, or imports a patented invention. But patent law also reaches parties who do not themselves perform every step of a claim yet are responsible for someone else's infringement. Those are the two indirect-infringement theories: induced infringement under § 271(b) and contributory infringement under § 271(c). Each is a separate cause of action with its own elements, and both depend on an underlying act of direct infringement by a third party.

Induced infringement is stated in a single sentence. Section 271(b) provides that "Whoever actively induces infringement of a patent shall be liable as an infringer." The operative word is "actively": liability attaches to affirmative conduct that encourages, instructs, or causes another to infringe — supplying directions to assemble a patented combination, marketing a product for an infringing use, or otherwise leading a third party to carry out the infringing acts.

"Whoever actively induces infringement of a patent shall be liable as an infringer."— 35 U.S.C. § 271(b), source

The knowledge requirement

The Supreme Court has read a knowledge element into inducement. In Global-Tech Appliances, Inc. v. SEB S.A. (2011), the Court held that induced infringement under § 271(b) requires knowledge that the induced acts constitute patent infringement, and that this knowledge requirement can be satisfied by willful blindness. In Commil USA, LLC v. Cisco Systems, Inc. (2015), the Court added that a good-faith belief that the patent is invalid is not a defense to inducement, because infringement and validity are distinct issues. The practical effect is that an accused inducer must know of the patent and intend the resulting infringement — ordinary negligence is not enough.

Contributory infringement is more specific and is aimed at component suppliers. Section 271(c) reaches whoever offers to sell, sells, or imports "a component of a patented machine, manufacture, combination or composition, or a material or apparatus for use in practicing a patented process, constituting a material part of the invention, knowing the same to be especially made or especially adapted for use in an infringement of such patent, and not a staple article or commodity of commerce suitable for substantial noninfringing use."

The substantial-noninfringing-use line

The defining limitation of contributory infringement is the staple-article carve-out. A supplier is not a contributory infringer if the component it sells is a staple article or commodity of commerce that is suitable for a substantial noninfringing use. A generic part with ordinary legitimate uses does not create liability; a component with no real use except in the infringing combination can. This is the principal doctrinal difference from inducement: contributory infringement turns on the objective character of the article supplied and whether it has substantial noninfringing uses, whereas inducement turns on the defendant's affirmative conduct and intent.

The two theories frequently appear together in the same complaint. A defendant that sells a specially adapted component and also provides instructions directing customers to use it in the patented way may face both a § 271(c) contributory claim and a § 271(b) inducement claim. Both still require a direct infringer: if no one actually carries out the patented method or assembles the patented combination, there is no indirect liability to attach. Claim terms in method and apparatus patents — for example, a "mesh routing module configured to" perform specified steps, as recited in U.S. Patent No. 9,479,428 — define the conduct that a third party must perform for indirect liability to follow.

Remedies for indirect infringement are the same as for direct infringement under § 284: damages adequate to compensate, no less than a reasonable royalty, with the possibility of enhanced damages for egregious conduct. Because inducement and contributory infringement both require proof of knowledge of the patent, the timing of notice — such as service of a complaint or a pre-suit letter identifying the patent — frequently marks the point from which indirect-infringement damages can run.

Proving the predicate direct infringement

Both indirect theories share a structural requirement that is easy to overlook: there must be an act of direct infringement by someone. The Supreme Court underscored this in Limelight Networks, Inc. v. Akamai Technologies, Inc. (2014), holding that there can be no liability for inducement under § 271(b) where no single actor has committed direct infringement of the method claim. A patentee asserting inducement must therefore identify a direct infringer — often the defendant's own customers — and show that those parties performed every step of the claimed method or used the patented combination.

This requirement intersects with how method claims are drafted. Where the steps of a claimed method are divided among multiple actors, a patentee may struggle to prove that any one party directly infringed, which in turn defeats the indirect claim. The Federal Circuit's later decisions on divided infringement addressed when one party can be held responsible for steps performed by another, but the baseline rule from Limelight remains: indirect liability is parasitic on a completed act of direct infringement.

The damages and notice consequences also distinguish the indirect theories in practice. Because § 271(b) and § 271(c) both require knowledge of the patent, the date a defendant learned of the patent — whether through a notice letter, a licensing approach, or service of the complaint — frequently fixes the start of the period for which indirect-infringement damages can be recovered. A defendant with no pre-suit knowledge may face indirect-infringement exposure only from the date of the complaint forward, which makes the knowledge timeline a central factual battleground in cases built on inducement or contributory infringement.