Someone Is Infringing My Patent — Now What?

Discovering a competitor selling something that looks a lot like your invention is infuriating — but the worst move is to react emotionally. Patent enforcement rewards preparation and punishes threats you can’t back up, so the smart response is methodical, not loud.

How do you confirm someone is actually infringing your patent?

The single biggest misconception in patent enforcement is that infringement means “they copied my product.” It doesn’t. Infringement is measured against the claims — the numbered sentences at the end of your patent that legally define what you own. Your product, your prototype, and your idea are all irrelevant to the analysis.

Confirming infringement is a two-step process courts follow, established in Markman v. Westview Instruments:

1. Claim construction. Determine what each word and phrase in the claim legally means. Courts read the claim in light of the specification and prosecution history, and this “Markman” interpretation often decides the whole case.
2. Comparison to the accused product. Apply the construed claim to the accused product, limitation by limitation.

The governing rule is the all-elements rule: a product infringes a claim only if it contains every single element (limitation) of that claim. Miss one limitation and there is no literal infringement. This is why attorneys build a claim chart — a two-column table with each claim limitation on the left and the corresponding feature of the accused product on the right, backed by evidence like photos, teardown analysis, source code, or the competitor’s own marketing.

Two kinds of infringement matter:

• Literal infringement — the accused product matches every limitation word-for-word as construed.
• Doctrine of equivalents — even if one element isn’t literally present, infringement can still exist if the accused product performs substantially the same function, in substantially the same way, to achieve substantially the same result. This doctrine is powerful but limited by “prosecution history estoppel,” which bars you from recapturing subject matter you gave up during examination.

Also identify who infringes and how: direct infringement under 35 U.S.C. §271(a), or indirect infringement — inducement (§271(b)) or contributory infringement (§271(c)) — where a party actively encourages or supplies components for another’s infringement. Indirect infringement requires proving the defendant knew of your patent and knew the induced acts were infringing, so notice (discussed below) becomes doubly important. Pinning down the right defendant early — the manufacturer, the importer, the reseller, or all three — shapes both your venue and your damages.

Is your own patent strong enough to enforce?

Before you accuse anyone, turn the microscope on yourself. Every enforcement action invites a counterattack on your patent’s validity, and a substantial share of asserted claims that reach a final decision are found invalid or not infringed — this is not a corner of law where the patent owner reliably wins. Ask honestly:

• Is the claim valid over the prior art? Could a defendant find a prior patent, publication, or product that anticipates (§102) or renders obvious (§103) your claim? This is the most common defense and the basis for most IPRs.
• Is the patent enforceable? Problems like inequitable conduct during prosecution, or improper inventorship, can render even a valid patent unenforceable.
• Do you have clean chain of title? You must own the patent (or hold an exclusive license) to sue. Assignment gaps are a frequent, avoidable problem — see who owns startup IP.
• What’s your damages story? Lost profits require proof you’d have made the sales; otherwise you’re limited to a reasonable royalty under §284.

If your claims are shaky, a demand letter may simply hand the other side a roadmap to kill your patent. Assessing validity candidly is the difference between leverage and a self-inflicted wound.

What are your options, from least to most aggressive?

Enforcement is a ladder, not a switch. Climb it deliberately.

• Monitor and document. If the infringement is minor or the infringer may design around, sometimes the right move is to keep dated records and watch. Delay generally won’t cost you the right to sue: the Supreme Court’s 2017 decision in SCA Hygiene Products v. First Quality Baby Products held that laches is no longer a defense to damages incurred within the statutory window, and patent law has no independent statute of limitations on filing. Instead, 35 U.S.C. §286 caps damages at six years before you file the complaint. Note that equitable estoppel — where you actively mislead an infringer into believing you won’t enforce, and they rely on it — can still bar a claim, so silence combined with affirmative signals is riskier than silence alone.
• Offer a license. Framing first contact as a business opportunity — “we hold patent X; let’s discuss a license” — is often cheaper, faster, and less legally dangerous than a threat, and it can turn an infringer into a paying partner. If licensing is your endgame, our how to license or sell a patent guide walks through structuring the deal.
• Send a cease-and-desist / demand letter. The classic formal step. Done right, it documents notice (which matters for damages) and opens negotiation; done wrong, it triggers a declaratory-judgment suit. We cover the drafting and traps in the patent cease-and-desist letter guide.
• Mediation or arbitration. A neutral-facilitated settlement can resolve the dispute for a fraction of litigation cost, and many parties prefer confidential resolution.
• File a Section 337 complaint at the ITC. If the infringing goods are imported, the U.S. International Trade Commission can issue an exclusion order barring them at the border — often faster (roughly 16–18 months) than district court and devastating to importers, though the ITC awards no money damages.
• File suit in federal district court. The full remedy set: injunctions (post-eBay v. MercExchange, no longer automatic), damages of at least a reasonable royalty, and up to treble damages for willful infringement under §284. It is also slow and expensive.

For the full strategic picture, start at our hub, the patent enforcement and monetization guide.

What are the risks of accusing someone of infringement?

Patent enforcement is one of the few areas where making the first move can put you on defense. Know the traps:

• Declaratory-judgment (DJ) jurisdiction. Once you create a “case of controversy” — typically by threatening suit or making a specific infringement charge — the recipient can file a declaratory-judgment action first, choosing a court and district favorable to them. That can strip you of your preferred venue and force you to litigate on their schedule.
• Inter partes review (IPR). The accused infringer can petition the Patent Trial and Appeal Board (PTAB) to cancel your claims on prior-art grounds. IPR uses a “preponderance of the evidence” standard — lower than a court’s “clear and convincing” — and cancels claims at a meaningful rate. Once you sue, the defendant generally has one year to file an IPR. Learn how these proceedings work in PTAB and IPR explained.
• Attorney-fee exposure. Under 35 U.S.C. §285, a court can award the prevailing party its attorney’s fees in an “exceptional” case. After Octane Fitness v. ICON lowered that bar, weak or bad-faith assertions can leave you paying the other side’s legal bills.
• Antitrust and bad-faith claims. Objectively baseless assertions made in bad faith can, in rare cases, strip your immunity and expose you to Walker Process or sham-litigation liability.

None of this means don’t enforce — it means enforce from strength, with your claim chart and validity analysis done first.

How does patent marking affect what you can recover?

This is the technical rule that quietly costs patent owners the most money. Under 35 U.S.C. §287, if you (or your licensees) sell products embodying the patent, you must mark them — with the word “patent” or “pat.” plus the patent number, or via virtual marking (“pat.” plus a freely accessible URL listing the patents) — to recover pre-suit damages.

If you don’t mark, you generally cannot collect damages for any infringement that happened before you gave the infringer actual notice (a specific charge of infringement) or filed suit. In practice, that can erase years of royalties. Key points:

• The marking requirement applies to products; a pure method/process patent with no product to mark is generally exempt.
• Actual notice must be specific — a vague “you might want to look at our patents” usually doesn’t count.
• Marking is an ongoing duty, and you bear the burden of proving compliance.

Audit your marking before you send any letter, because the date notice attaches is the date your damages clock may start.

What does it actually cost and how long does it take?

Full-blown patent litigation is among the most expensive disputes in U.S. law. Depending on the amount in controversy, cases routinely run into the hundreds of thousands to several million dollars through trial, and take two to three years or more. IPRs, ITC actions, and settlements each carry their own cost and timeline profiles. Before committing, read patent litigation cost and timeline so the budget matches the stakes — a $50,000 problem rarely justifies a $2 million lawsuit.

This economic reality is exactly why the options ladder matters: licensing, mediation, and well-targeted demand letters resolve most disputes without ever reaching a courtroom.

Should you handle this yourself or hire counsel?

Patent enforcement is not a DIY project. The claim-construction analysis, validity assessment, and declaratory-judgment/venue strategy all turn on doctrine that changes with every Federal Circuit and Supreme Court term. Even the seemingly simple act of sending a letter can forfeit your venue or trigger fee exposure.

A patent litigator (or IP-enforcement counsel) will typically start by building the claim chart and a validity opinion, then help you choose the right rung on the ladder. Many take strong cases on contingency or hybrid fees, which also serves as a candid third-party read on how good your case really is. To see how these fights actually unfold, browse our patent case analysis archive.

The bottom line

When someone infringes your patent, resist the urge to threaten and instead do the unglamorous work first: construe your claims, build an element-by-element claim chart proving every limitation is met, and stress-test your own patent for validity and IPR exposure. Confirm you’ve complied with the §287 marking statute so your damages reach as far back as possible. Then climb the options ladder deliberately — monitor, license, demand, mediate, ITC, or sue — matching the response to the size of the problem. Enforced from strength, a patent is a powerful asset; asserted carelessly, it can become a liability that hands your competitor the tools to destroy it.

This guide is general education, not legal advice, and does not create an attorney-client relationship. Patent infringement, validity, and enforcement strategy turn on your specific claims and facts, and a misdirected demand letter can create real legal exposure — consult an attorney licensed in your jurisdiction before acting.