You Received a Patent Demand Letter — Here Is What It Actually Means

A letter arrives claiming your product infringes someone's patent and demanding a licensing fee or threatening a lawsuit. Your first instinct may be to panic or dismiss it. Neither is the right move — demand letters sit on a spectrum from serious litigation threats to mass-mailed fishing expeditions, and knowing which kind you are dealing with shapes everything that follows.

What a Demand Letter Actually Is

A patent demand letter is a written notice from a patent owner (or their attorney, or a licensing entity acting on their behalf) asserting that your product or service infringes one or more claims of a specific patent. It typically asks you to take a license, stop the accused activity, or both.

Demand letters are not lawsuits. They carry no immediate legal force on their own. But they do start a clock in one important way: once you have received actual notice of a patent and continued using the technology, a court can treat that period as willful infringement if you later lose at trial. Willful infringement can support enhanced damages — up to three times the base award under current law. Ignoring a letter is rarely the free option it appears to be.

Who Sends Them

Demand letters come from several types of senders, and the type matters:

• Operating companies that actually make products and view your activity as competitive harm. These senders often want market behavior to change, not just a royalty check.
• Patent assertion entities (PAEs), sometimes called patent trolls, whose business model is licensing revenue. They frequently send high volumes of letters and settle for amounts below the cost of litigation.
• Universities and research institutions that patent discoveries and license them as a revenue stream.
• Individual inventors who hold a patent and believe a company is using their idea without compensation.

The sender's identity and business model influence their willingness to litigate, the license fees they will accept, and how much leverage you actually have.

How to Evaluate the Letter

Before responding in any way — including by phone — get the letter in front of a patent attorney. What you say early can matter later. Once you have counsel involved, the evaluation typically covers three questions.

Does the Patent Cover What You Actually Do?

This is a claim construction question. Patent protection is defined by the claims, not the abstract or the drawings. A demand letter will cite specific claim numbers. Each element of a claim must be present in your product for that claim to be infringed. Many demand letters assert broadly and hope the recipient does not read the claims carefully. A technical analysis comparing the accused product to each claimed element — sometimes called a claim chart — is the standard tool for this evaluation.

Is the Patent Valid?

A granted patent is presumed valid, but that presumption can be overcome. Prior art that the USPTO did not consider during examination, or prior art that was cited but arguably not properly weighed, can form the basis of an invalidity argument. Inter partes review (IPR) at the USPTO is one formal mechanism for challenging validity without going to district court. Invalidity is a defense, not a guarantee — but a credible invalidity position changes the negotiating dynamic significantly.

What Is the Cost-Benefit of Each Path?

Your realistic options after evaluation are: negotiate a license, design around the patent, challenge validity (formally or as leverage in negotiation), litigate if sued, or some combination. Each path has a different cost, timeline, and risk profile. A nuisance-value settlement may be rational even when you believe you do not infringe, because litigation is expensive and disruptive. That calculus changes when the demanded royalty is large, when the patent owner is a serial litigant, or when your core product is at stake.

What Not to Do

• Do not respond to the letter yourself before speaking with a patent attorney. Admissions and characterizations made in early correspondence can resurface in litigation.
• Do not destroy or alter records related to your product's development. Litigation hold obligations can attach once you receive notice of a credible threat.
• Do not assume a low demanded royalty means low risk. Some demand campaigns use low initial figures to generate volume settlements and then escalate with repeat senders.
• Do not publicly disparage the patent owner in ways that could be used against you. Keep early communications professional and through counsel.

Practical Takeaways

• A demand letter is not a lawsuit, but it is not nothing — it starts the willful infringement clock.
• Read the actual claims, not just the letter; many assertions are weaker than they appear once you compare claims to your product element by element.
• The sender's identity and business model are relevant inputs to your response strategy.
• Invalidity and non-infringement are separate defenses; both are worth evaluating before you respond.
• Early communications with the patent owner should go through counsel — what you say informally can matter later.
• The right path forward depends on the strength of the patent, the size of the demand, and the realistic cost of each option, not on instinct alone.

This guide is general education, not legal advice, and does not create an attorney–client relationship. For your specific situation, talk to a registered patent attorney.