Received a Patent Demand Letter? The First 72 Hours
The letter says your product infringes someone's patent. It names a deadline, and it may demand that you stop selling, take a license, or pay for past sales.
What you do in the next three days shapes everything after it. Done well, those days preserve your options and put you in a position to respond from analysis rather than alarm. Done badly, a hasty reply or a careless email can become evidence against you.
This is a practical checklist for the first 72 hours, written for founders, executives and in-house teams. It is general information, not legal advice for your situation.
Day 1: Preserve and contain
Keep everything. Save the letter, the envelope or email headers, and any attachments or claim charts. Write down the date you received it and any response date it sets.
Keep the circle small. Tell only the people who need to know. Ask them not to discuss whether the product infringes in email, chat or text. Those messages are often discoverable if a lawsuit follows, and offhand speculation reads badly later.
Hold off on replying. A quick "we don't infringe" or "let's talk" can lock in positions before anyone has read the claims. Acknowledging receipt is rarely urgent. Getting the substance right is.
Day 2: Read the letter and the patent
Start with what kind of letter it is. Some letters only offer a license and identify the patent. Others accuse a specific product and claim, attach a claim chart, or threaten suit. The more specific the letter, the more seriously it should be treated.
Then check the basics of the patent itself. Each takes minutes, and any one can change the picture:
Is it in force? Check the expiration date and whether maintenance fees have been paid. An expired patent can still support a claim for past damages, but it can't stop future sales.
Who owns it? Compare the letter's sender with the USPTO assignment records.
Which claims are asserted? Read them yourself. The claims, not the title or abstract, define what the patent covers.
Which product is accused? Identify the exact version and when it was first made, sold or imported.
What else is in the family? Note any continuations, and whether the patent has been through ex parte reexamination or an earlier IPR. That history often limits what the claims can mean.
Day 3: Start the real analysis
By the third day, the question is whether the letter has merit. That takes a claim-by-claim review by a patent attorney, usually leading to a written opinion. A useful opinion looks at three things:
Non-infringement. Each asserted claim is compared, element by element, with how your product actually works. One missing element is enough to avoid literal infringement of that claim.
Invalidity. Prior art is searched and analyzed to test whether the claims should have issued as written.
The file history. The prosecution history at the USPTO shows what the patent owner argued and gave up to get the claims allowed. Those statements can narrow the claims, sometimes decisively. When the record includes continuations, reexaminations or earlier IPR challenges, this is often where the strongest answer is found.
To start, the reviewer needs the letter, the patent number, and a way to understand the product: specifications, technical documents, or a walkthrough. You don't need to prepare a legal brief.
Mistakes to avoid
Ignoring it. Silence rarely makes a patent owner go away, and a missed deadline can push them toward filing suit.
Replying in a hurry. Don't admit or flatly deny infringement before the claims have been analyzed.
Calling the patent owner to "clear it up." Informal conversations create a record you don't control.
A quick redesign. Renaming or tweaking the product without checking the claims may not avoid them, and can look like an admission.
Letting the date pass in silence. If you need more time, ask for it in writing, through counsel.
Why the letter raises the stakes: willfulness
A demand letter puts you on notice of the patent. Knowledge of the patent is a key ingredient of willful infringement.
If infringement is later found to be willful, a court can increase damages up to three times under 35 U.S.C. § 284. In exceptional cases it can also award attorney fees under § 285. Since the Supreme Court's 2016 decision in Halo Electronics v. Pulse Electronics, courts reserve enhanced damages for egregious conduct, judged on the facts of each case.
Two points are often misunderstood:
Not getting an opinion is not proof of willfulness. Under 35 U.S.C. § 298, failing to obtain advice of counsel, or failing to show it to the court, may not be used to prove willful infringement.
Getting one still helps. A timely, competent opinion gives you a sound basis for your decisions about the product. If you choose to rely on it later, it can be strong evidence of good faith. Whether and how to rely on it is a decision to make with your counsel.
Next step
The best time to understand a demand letter is before you answer it. Patent Intelligence Group provides confidential, claim-by-claim non-infringement and invalidity opinions for companies that have received one, including patents with complex file histories.
Request a confidential review of your letter.
General information only. This article is not legal advice, does not create an attorney-client relationship, and is not a prediction of any outcome.
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