35 U.S.C. § 271
Patent infringement: no filing deadline, but a six-year limit on what you can collect
A federal claim in United States district courts · Last verified August 26, 2026
Nearly every source that lists patent infringement alongside other federal claims gets one thing wrong, and it is the same thing: patent law has no statute of limitations.
There is a six-year provision. It does not bar the suit. It limits how far back the damages reach. The difference is worth real money, and getting it backwards costs plaintiffs claims they still had.
What the claim is
Someone made, used, sold, offered to sell, or imported your patented invention without permission.
Most cases are companies suing competitors. A meaningful share are brought by entities that own patents and do not make anything, whose economics depend on the cost of defending rather than the merits. Both kinds run through the same statute.
The claim is heard in federal district court exclusively — no state court has jurisdiction — and every appeal goes to a single court, the Federal Circuit, which is why patent law is more uniform than most federal law on this site.
Where the right comes from
Direct infringement is defined expressly:
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.
Separate provisions reach induced infringement — encouraging someone else to infringe — and contributory infringement, selling a component with no substantial non-infringing use. A short companion section supplies the vehicle: "A patentee shall have remedy by civil action for infringement of his patent."
What a plaintiff has to prove
For direct infringement, two elements:
- A valid, enforceable patent the plaintiff owns.
- The accused product or process meets every limitation of at least one claim — either literally, or under the doctrine of equivalents.
Every limitation. Missing one element of a claim means no infringement, however similar the products look. This is what makes claim construction — deciding what the patent's words mean — the decisive event in most cases. It is a question of law for the judge, with subsidiary factual findings, and it happens well before trial.
Direct infringement is strict liability. Knowing about the patent is not required, and neither is intent.
Indirect infringement is different and requires knowledge. Induced infringement needs direct infringement by someone else, knowledge of the patent, and specific intent to encourage the infringement. Willful blindness will satisfy the knowledge element.
The Supreme Court tightened what must be pleaded for inducement in Hikma Pharmaceuticals USA Inc. v. Amarin Pharma, Inc. (2026), holding unanimously that a patent owner must plausibly allege statements designed to stimulate others to infringe; statements that merely could stimulate others are not enough.
How long you have to file
There is no deadline to file. Read the provision people mistake for one:
Except as otherwise provided by law, no recovery shall be had for any infringement committed more than six years prior to the filing of the complaint or counterclaim for infringement in the action.
It runs backward from the filing date, and it limits recovery. It does not bar the action. If a company has been infringing for ten years and you sue today, you may still sue, you may still get an injunction, and you may recover damages for the most recent six years.
Each act of infringement is a separate claim with its own accrual.
Laches is no longer available to bar damages inside the six-year window. The Supreme Court held so in SCA Hygiene Products Aktiebolag v. First Quality Baby Products, applying the reasoning it had used in copyright.
What has to happen before you file
Nothing administrative. But there is a notice requirement that behaves like a prerequisite for anyone who sells a product.
Marking. A patentee who sells a physical product covered by the patent — or whose licensees do — must mark it with the patent number. Virtual marking, a label pointing to a webpage listing the patents, is permitted.
Fail to mark and you cannot recover damages for infringement occurring before the infringer got actual notice — a cease-and-desist letter, or the complaint itself. Years of infringement can evaporate this way.
Two limits worth knowing: marking does not apply to method or process patents, and the requirement operates as a limit on damages, not a bar to filing.
Who can be sued — and who cannot
Anyone who makes, uses, sells, offers to sell, or imports the invention. Customers can be defendants, which is a pressure tactic as much as a legal position.
Standing requires all substantial rights. The patentee or an exclusive licensee may sue. A bare non-exclusive licensee cannot.
States have sovereign immunity from patent infringement suits.
An accused infringer has a second front available: challenging the patent's validity at the Patent Trial and Appeal Board through inter partes review, often while asking the district court to stay the litigation. That parallel track is a defining feature of modern patent practice.
Common defenses
Non-infringement — the accused product omits at least one claim limitation.
Invalidity, on any of several grounds: the invention was not new, it was obvious, the patent fails to enable or describe what it claims, or it claims ineligible subject matter such as an abstract idea. The enablement requirement was strengthened in Amgen Inc. v. Sanofi (2023), which held that a patent claiming an entire class of compounds must enable a skilled person to make and use the whole class without unreasonable experimentation.
Invalidity must be proven by clear and convincing evidence — issued patents carry a presumption of validity.
Inequitable conduct — fraud on the Patent Office during prosecution, requiring but-for materiality and specific intent. It renders the whole patent unenforceable, which is why it is pleaded often and proven rarely.
Patent exhaustion, which ends the patentee's rights in a particular item once it is sold.
Failure to mark, and the six-year damages limit.
What the claim pays
Damages adequate to compensate, and in no event less than a reasonable royalty. Lost profits are available where the patentee can show it would have made the sales.
Enhanced damages up to three times the amount assessed, for egregious or willful infringement. The Supreme Court loosened the test in Halo Electronics v. Pulse Electronics, replacing a rigid two-part standard with district court discretion.
Injunctions, but not automatically. For most of patent history a winning patentee got one as a matter of course. eBay Inc. v. MercExchange ended that, requiring the ordinary four-factor equitable showing. The practical consequence is large: a plaintiff who does not compete with the defendant often cannot show irreparable harm, and ends up with a royalty instead of the leverage an injunction would supply.
Attorney's fees in exceptional cases only — a case standing out from others in the strength of a party's position or the manner of litigation, decided case by case.
What people get wrong
"There's a six-year statute of limitations to file a patent suit." No. There is no filing deadline. The six-year provision limits how far back damages reach.
"Laches will bar the claim if they waited." Not for damages inside the six-year window.
"I invented it independently, so I'm safe." Independent invention is not a defense to direct infringement. The statute imposes strict liability, subject to a narrow prior-user right.
"They didn't know about my patent, so they didn't infringe." Knowledge is irrelevant to direct infringement. It matters for inducement and for enhanced damages.
"If I win, I get an injunction." Not since eBay.
"The patent is presumed valid, so it can't be invalidated." The presumption is rebuttable, by clear and convincing evidence — and it can be attacked at the Patent Office on a lower standard.
"Their product is nearly identical, so it infringes." Every limitation of a claim has to be met. Similarity is not the test.
Where it came from
The Patent Act of 1952 codified title 35 and gave the statute its modern shape, including the provision defining infringement and the obviousness requirement.
The Leahy-Smith America Invents Act of 2011 was the largest change in decades. It moved the United States from first-to-invent to first-inventor-to-file, aligning with the rest of the world, and created the Patent Trial and Appeal Board with its post-grant review procedures. Those procedures reshaped litigation strategy: a defendant now has a cheaper, faster forum in which to attack validity, and district court cases are routinely stayed while that plays out.
Common questions
Is there a statute of limitations for patent infringement?
No. There is no deadline to file. Section 286 limits damages to infringement committed within six years before the complaint, but it does not bar the suit itself.
Can I sue over infringement that started ten years ago?
Yes. You can file, seek an injunction, and recover damages for the most recent six years. Laches will not bar damages inside that window.
Do I have to mark my product with the patent number?
If you sell a physical product covered by the patent, yes — otherwise you cannot recover damages for infringement that occurred before the infringer received actual notice. Marking does not apply to method or process patents.
Is independent invention a defense?
Generally no. Direct patent infringement is strict liability, so developing the same thing on your own does not excuse it. A narrow prior-user right exists in limited circumstances.
Will I get an injunction if I win?
Not automatically. Since eBay Inc. v. MercExchange, a patentee must satisfy the traditional four-factor equitable test, and plaintiffs who do not compete with the defendant often cannot.