What is patent infringement?
Patent infringement is the unauthorized use of a patented invention, violating a patent holder's rights. It arises when someone practices a patented invention without the patent owner's permission and while the patent is in force.
What a patent grants
A U.S. patent gives the patent owner the right to exclude others from making, using, offering for sale, selling, or importing an invention into the U.S. for a limited time. Under 35 U.S.C. § 271(a), whoever without authority makes, uses, offers to sell, or sells any patented invention within the United States, or imports any patented invention into the United States during the term of the patent, infringes the patent.
The prohibited acts span the full commercial chain. Making, using, offering to sell, selling, and importing are each independently actionable under the statute, so a party who manufactures a patented product without authorization infringes even if no sale ever takes place.
The element-by-element test
Infringement is not tested against the patent as a whole. Analysis proceeds claim by claim, and an accused product or process is compared against each claim separately. Infringement occurs when someone makes, uses, offers to sell, sells, or imports a product or process containing every element of a patented claim or its equivalent while the patent remains valid.
Two routes to infringement exist.
Literal infringement means that every element recited in a claim is present in the accused product or process exactly as written. If even one element is absent, there is no literal infringement of that claim.
The doctrine of equivalents extends coverage beyond the exact claim language. The doctrine is designed to prevent an infringer from stealing the benefit of a patented invention by changing only minor or insubstantial details. Under this doctrine, a device or process infringes if it performs substantially the same function in substantially the same way to obtain the same result as the claimed element.
The doctrine is bounded by the all-elements rule: equivalency must be applied to each individual claim element, not the invention as a whole, and every patented element must have a substantial equivalent in the accused product. Equivalency is assessed at the time of the alleged infringement, not at the time the patent was issued.
Direct, induced, and contributory infringement
Direct infringement
Section 271(a) reaches anyone who commits an infringing act (making, using, selling, offering, or importing) without authority during the patent term. Intent and good faith are generally not a defense to the underlying act of direct infringement.
Induced infringement
Under 35 U.S.C. § 271(b), whoever actively induces infringement of a patent shall be liable as an infringer. Induced infringement is indirect: it requires that a third party commits direct infringement and that the defendant actively encouraged or assisted that infringing act.
Contributory infringement
Under 35 U.S.C. § 271(c), whoever offers to sell or sells within the United States or imports into the United States a component constituting a material part of a patented invention, knowing it to be especially made or especially adapted for use in an infringement and not a staple article or commodity of commerce suitable for substantial noninfringing use, shall be liable as a contributory infringer. The "not a staple article" limitation is consequential: a general-purpose component with substantial lawful uses is not a basis for contributory infringement, even when the seller knows some buyers will use it to infringe.
Defenses
Non-infringement
The most direct defense is that the accused product or process does not contain every element of any asserted claim, either literally or under the doctrine of equivalents. If the accused party establishes this for every asserted claim, it avoids liability entirely.
Invalidity
A patent is presumed valid, and the party challenging its validity bears the burden of proof. Defenses available in a patent infringement action include noninfringement, invalidity under Part II of Title 35, unenforceability, and failures of required disclosure or procedural compliance. An infringer who proves a claim invalid escapes liability on that claim, even when the accused product falls within the claim's literal scope.
Patent exhaustion
The doctrine of patent exhaustion limits a patent holder's ability to enforce a patent after an authorized sale of the patented item. Once a patented article has been sold with the patent owner's authorization, the patent rights in that particular article are exhausted and the buyer may use or resell it without further permission from the patent holder.
Remedies
A patentee has the right to seek remedy by civil action for infringement of the patent. Courts may award three categories of relief.
Injunctions: Courts may grant injunctions in accordance with the principles of equity to prevent the violation of any right secured by patent, on such terms as the court deems reasonable. Injunctive relief is sought to stop ongoing or threatened infringement.
Damages: Damages must be adequate to compensate for the infringement, but in no event less than a reasonable royalty for the use made of the invention by the infringer. Courts may also increase the damages award up to three times the amount found or assessed.
Attorney fees: In exceptional cases, the court may award reasonable attorney fees to the prevailing party. This provision is available to either the patent holder or the accused infringer who prevails.
Forms and remedies at a glance
| Form | Basis | What the plaintiff must show |
|---|---|---|
| Direct | 35 U.S.C. § 271(a) | Accused party performed an infringing act during the patent term without authority |
| Induced | 35 U.S.C. § 271(b) | Accused party actively induced a third party's direct infringement |
| Contributory | 35 U.S.C. § 271(c) | Accused party sold or imported a non-staple material component adapted for infringement, with knowledge |
| Remedy | Basis | Notes |
|---|---|---|
| Injunction | 35 U.S.C. § 283 | Equitable; courts weigh hardships and public interest |
| Damages | 35 U.S.C. § 284 | Floor: reasonable royalty; ceiling: 3x enhanced damages |
| Attorney fees | 35 U.S.C. § 285 | Available to either side in exceptional cases |
Practical notes
- Analyze each asserted claim separately. An infringement finding requires that the accused product or process satisfy every element of at least one asserted claim. A product may infringe some claims but not others; evaluating each one individually is essential.
- Evaluate both literal infringement and the doctrine of equivalents. A defendant who redesigns to avoid literal infringement may still face doctrine of equivalents exposure if the change is insubstantial. Plaintiffs should assess both theories before concluding that no infringement occurred.
- Indirect infringement requires a direct infringer. There is no induced or contributory infringement without an underlying act of direct infringement by a third party. This shapes both the theory of the case for the plaintiff and the strategic options available to the defendant.
- Good faith is not a defense to liability, but it can affect damages. Direct infringement does not require intent. However, evidence that a defendant continued to infringe after becoming aware of the patent can affect the court's exercise of its discretion to enhance damages under § 284.
- Invalidity is an affirmative defense, not a freebie. The presumption of validity under § 282 places the burden on the accused infringer. A court finding of invalidity eliminates liability for that claim without requiring proof of non-infringement, but reaching that result requires meeting a demanding evidentiary standard.