Patent Infringement Demand Letters

35 U.S.C. §§ 271, 281-285 – Patent Act

Related Patent Enforcement Templates

Federal Patent Infringement Law
Patent Protection: Patents grant inventors the right to exclude others from making, using, selling, offering to sell, or importing their invention for a limited time (20 years from filing for utility patents, 15 years from grant for design patents). Unlike trademarks, patent rights require federal registration—there are no common-law patent rights.
Types of Patents
Patent Type Protects Term Requirements
Utility Patent New and useful process, machine, manufacture, or composition of matter 20 years from filing Novel, non-obvious, useful, enabled
Design Patent New, original, ornamental design for an article of manufacture 15 years from grant Novel, non-obvious, ornamental (not functional)
Plant Patent New variety of asexually reproduced plant 20 years from filing Novel, non-obvious, distinct
Types of Infringement – 35 U.S.C. § 271
Type Statute Elements
Direct Infringement § 271(a) Making, using, selling, offering to sell, or importing the patented invention without authority
Induced Infringement § 271(b) Actively inducing another to directly infringe, with knowledge of the patent and intent to cause infringement
Contributory Infringement § 271(c) Selling a component with no substantial non-infringing use, knowing it will be used to infringe
Importation of Infringing Goods § 271(a) Importing into U.S. products that infringe U.S. patent claims
Remedies – 35 U.S.C. §§ 281-285
Remedy Statute Details
Compensatory Damages § 284 Damages adequate to compensate for infringement, not less than a reasonable royalty
Lost Profits § 284 Available if patent owner can prove: demand for product, absence of acceptable substitutes, manufacturing capability, and quantifiable profits lost
Enhanced Damages § 284 Up to 3x damages for willful infringement (Halo v. Pulse standard)
Attorney Fees § 285 In "exceptional cases" (litigation misconduct, bad faith, willfulness)
Injunctive Relief § 283 Permanent injunction after eBay four-factor test; preliminary injunctions if likelihood of success
Prejudgment Interest § 284 Interest from date of infringement to judgment
Patent Marking – § 287: If you sell patented products without proper marking (patent number on product/packaging, or virtual marking via URL), you can only recover damages from the date of actual notice to infringer—typically the demand letter date. Proper marking allows damages from when infringement began.
Statute of Limitations
  • 35 U.S.C. § 286: Cannot recover damages for infringement more than 6 years before filing suit
  • Laches: Unreasonable delay in filing suit can bar damages (but not injunction) for period of delay
  • No criminal penalties: Unlike copyright/trademark, patent infringement is purely civil
Patent Claim Analysis & Infringement
The Claim Is Everything

Patent infringement analysis centers on the claims—the numbered paragraphs at the end of the patent that define the legal scope of protection. Each claim element must be present in the accused product for infringement to exist.

All-Elements Rule: To prove infringement, the accused product or method must practice every limitation of at least one claim. If any claim element is missing, there is no literal infringement of that claim.
Claim Construction

Before comparing claims to accused products, claim terms must be interpreted. Courts use:

  • Plain and ordinary meaning: How a person of ordinary skill in the art would understand the term
  • Specification (description): The patent's detailed description can limit or clarify claim scope
  • Prosecution history: Arguments made to USPTO can limit claim scope (prosecution history estoppel)
  • Extrinsic evidence: Technical dictionaries, expert testimony (secondary to intrinsic evidence)
Claim Chart Template

A claim chart maps each claim element to corresponding features in the accused product:

Claim Element Patent Language Accused Product Feature
Preamble "A device for processing data comprising:" The [Product Name] is a device that processes data...
Element 1a "a processor configured to receive input signals;" [Product] includes an ARM processor that receives input signals from sensors...
Element 1b "a memory storing instructions;" [Product] contains 8GB flash memory storing firmware instructions...
Element 1c "wherein the processor executes the instructions to generate output." The ARM processor executes stored instructions to generate display output...
Literal Infringement vs. Doctrine of Equivalents
Theory Test Application
Literal Infringement Accused product includes every claim element exactly as written Word-for-word match; element present or absent
Doctrine of Equivalents Function-Way-Result test: performs substantially same function, in substantially same way, to achieve substantially same result Catches minor variations designed to evade literal claim language
Prosecution History Estoppel Cannot recapture under DOE what was surrendered during prosecution If claim was narrowed to overcome prior art, DOE limited
Independent vs. Dependent Claims
  • Independent claims: Stand alone; define invention without reference to other claims
  • Dependent claims: Incorporate all limitations of parent claim plus additional limitations; narrower scope
  • Strategy: Focus demand letters on broadest independent claims; include dependent claims that add features clearly present in accused product
Evidence to Gather
  • Accused product: Purchase and photograph/document; obtain user manuals, spec sheets
  • Teardown analysis: If necessary, disassemble to identify internal components
  • Marketing materials: Defendant's website, brochures describing product features
  • Source code: For method/software patents, may need discovery (not available pre-suit)
  • Expert analysis: Technical expert can prepare claim chart and infringement opinion
Avoid Overreaching: Demand letters based on weak claim charts can backfire. If claim construction is uncertain or elements are missing, a court may find non-infringement and potentially award fees to defendant as an "exceptional case." Do thorough analysis before sending demands.
Drafting Patent Demand Letters
Strategic Goals
  • Establish actual notice: Triggers potential willfulness and starts § 287 damages clock if no marking
  • Cease manufacturing and sales: Stop ongoing infringement
  • Accounting of sales: Obtain information for damages calculation
  • Monetary compensation: Past royalties, lost profits, or lump-sum settlement
  • Licensing agreement: Ongoing royalties for continued authorized use
  • Recall/destruction: Remove infringing products from market
Essential Components
Section Content
Patent identification Patent number(s), title, issue date, current ownership/assignee status
Patent validity Maintenance fees paid; any IPR/reexamination survived; not expired
Accused product identification Specific product name, model number, where sold
Infringement analysis Reference to claim chart (attached or described); identify claims infringed
Acts of infringement Making, using, selling, offering for sale, importing—which apply
Willfulness warning This letter provides actual notice; continued infringement may be willful
Damages exposure Reasonable royalty, lost profits, enhanced damages, attorney fees
Demand Cease by [date]; provide sales accounting; discuss licensing or settlement
Response deadline Typically 14-30 days
Tone Considerations
  • Professional, not threatening: Courts disfavor bullying tactics
  • Factual, not conclusory: Show you've done the analysis
  • Open to dialogue: Many patent disputes settle with licensing; leave door open
  • Proportionate: Match tone to severity—innocent small business vs. deliberate copyist
Attach or Describe Claim Chart?
  • Attach full claim chart: Strongest approach; shows seriousness; educates recipient
  • Describe without attachment: Preserves some flexibility; avoids detailed rebuttal in response
  • Reference available upon request: Middle ground; shows work is done without revealing details
Declaratory Judgment Risk: A patent demand letter creates "case or controversy" allowing recipient to file DJ action seeking declaration of non-infringement/invalidity. Consider: (1) forum selection—where would you want to litigate? (2) strength of claims—if weak, DJ exposes you to adverse ruling.
Special Considerations
  • Customer letters: Sending demands to infringer's customers is risky—may be tortious interference or defamation if patent is invalid; proceed cautiously
  • Multiple defendants: Manufacturer vs. distributors vs. retailers—often target manufacturer first
  • International infringers: U.S. patents only enforceable in U.S.; consider ITC 337 exclusion orders for imports
  • NPE considerations: Non-practicing entities face more scrutiny; emphasize legitimate innovation
Pre-Suit Requirements
  • No formal requirement: Unlike some claims, you can sue for patent infringement without prior demand
  • But demand is advisable: Establishes notice, shows good faith, may resolve without litigation costs
  • Preserve evidence: Screenshot website, purchase product, document pricing before sending letter (evidence may disappear)
Sample Patent Demand Letters
Sample 1: Standard Patent Infringement Demand
[Your Company / Law Firm] [Address] [Email / Phone] [Date] VIA CERTIFIED MAIL AND EMAIL [Defendant Company Name] [Address] Attn: General Counsel / CEO Re: Infringement of U.S. Patent No. [X,XXX,XXX] – Demand for Immediate Cessation Dear [Recipient]: I represent [Patent Owner], the owner of United States Patent No. [X,XXX,XXX] (the "'XXX Patent"), entitled "[Patent Title]," a copy of which is enclosed. The 'XXX Patent was duly issued by the United States Patent and Trademark Office on [Issue Date] and remains in full force and effect. PATENT OVERVIEW The 'XXX Patent covers [brief, non-technical description of invention]. [Patent Owner] invested substantial resources developing this technology and has commercialized it through [products/licensing]. INFRINGEMENT We have become aware that [Defendant] is making, using, selling, and/or offering for sale a product known as "[Accused Product Name]" that infringes one or more claims of the 'XXX Patent. A preliminary claim chart comparing independent claim 1 of the 'XXX Patent to [Defendant]'s [Accused Product] is attached as Exhibit A. As demonstrated in the claim chart, the [Accused Product] practices each and every element of claim 1. Specifically, [Accused Product]: • [Element 1 - brief description of how product meets claim element] • [Element 2 - brief description] • [Element 3 - brief description] LEGAL CONSEQUENCES [Defendant]'s unauthorized manufacture and sale of the [Accused Product] constitutes infringement under 35 U.S.C. § 271(a). This letter provides [Defendant] with actual notice of the 'XXX Patent and [Defendant]'s infringement. Continued infringement after receipt of this letter may be deemed willful, subjecting [Defendant] to: • Compensatory damages, including lost profits and/or a reasonable royalty (35 U.S.C. § 284); • Enhanced damages up to three times actual damages for willful infringement; • Attorney fees and litigation costs (35 U.S.C. § 285); • Permanent injunction prohibiting future infringement (35 U.S.C. § 283). DEMAND To avoid federal litigation, we demand that [Defendant]: 1. Immediately cease all manufacture, use, sale, offer for sale, and importation of any products infringing the 'XXX Patent; 2. Provide a written accounting of all [Accused Product] units manufactured, sold, and currently in inventory, along with revenue and profit attributable to those sales; 3. Contact the undersigned within fourteen (14) days of receipt of this letter to discuss resolution, which may include a licensing arrangement or monetary settlement. [Patent Owner] reserves all rights, including the right to seek damages for past infringement and to file suit without further notice if this matter is not resolved promptly. We prefer to resolve this matter without litigation. Please contact me directly at [Phone] or [Email] to discuss. Sincerely, [Attorney Name] [Firm Name] Counsel for [Patent Owner] Enclosures: - Copy of U.S. Patent No. X,XXX,XXX - Exhibit A: Claim Chart
Sample 2: Licensing-Focused Patent Demand
[Your Company] [Address] [Email / Phone] [Date] [Defendant Company] [Address] Attn: Licensing / Business Development Re: U.S. Patent No. [X,XXX,XXX] – Licensing Inquiry Dear [Recipient]: [Patent Owner] is the owner of a portfolio of patents covering [technology area], including U.S. Patent No. [X,XXX,XXX] (the "'XXX Patent"). We have identified [Defendant]'s [Product Line] as potentially practicing certain claims of our patents. Rather than pursue enforcement litigation, we are reaching out to explore a mutually beneficial licensing arrangement. OUR TECHNOLOGY The 'XXX Patent covers [description of innovation]. [Patent Owner] has licensed this technology to [X] companies in the [industry], establishing a reasonable royalty rate of approximately [X]% of net sales. POTENTIAL OVERLAP Our preliminary analysis indicates that [Defendant]'s [Product] may practice claims [1, 5, and 12] of the 'XXX Patent. We would welcome the opportunity to present our technical analysis and discuss [Defendant]'s products in more detail. PROPOSED NEXT STEPS We propose: 1. A confidential technical meeting (in person or video) where we present our claim charts and [Defendant] presents any non-infringement or invalidity positions; 2. If overlap is confirmed, negotiation of a license agreement on commercially reasonable terms consistent with our existing licensee agreements; 3. A standstill period of [60] days during which neither party will initiate litigation while we negotiate in good faith. We believe a licensing arrangement serves both parties' interests better than costly litigation. Our licensing terms are reasonable and have been accepted by major industry participants. Please contact me by [Date] to arrange an initial discussion. Sincerely, [Your Name] [Title] [Contact Info]
Sample 3: Willful Infringement Escalation
[Law Firm Letterhead] [Date] VIA CERTIFIED MAIL, RETURN RECEIPT REQUESTED [Defendant Company] [Address] Attn: General Counsel Re: FINAL NOTICE – Willful Infringement of U.S. Patent No. [X,XXX,XXX] Dear [Recipient]: This firm represents [Patent Owner] regarding your company's continuing infringement of U.S. Patent No. [X,XXX,XXX] (the "'XXX Patent"). PRIOR NOTICE By letter dated [Prior Letter Date], we notified [Defendant] that its [Product] infringes the 'XXX Patent and demanded that [Defendant] cease infringement. [Defendant] [has not responded / responded by denying infringement without substantive analysis / responded but failed to cease infringement]. CONTINUED WILLFUL INFRINGEMENT Despite actual knowledge of the 'XXX Patent and its infringement, [Defendant] continues to manufacture, advertise, and sell the [Product]. [Defendant]'s [Product] remains for sale on [website/retail channels], and we have confirmed recent sales as of [Date]. This continued infringement with knowledge of the patent constitutes willful infringement under Halo Electronics, Inc. v. Pulse Electronics, Inc., 579 U.S. 93 (2016). Willful infringement exposes [Defendant] to: • ENHANCED DAMAGES of up to THREE TIMES actual damages (35 U.S.C. § 284); • ATTORNEY FEES as an exceptional case (35 U.S.C. § 285); • PERMANENT INJUNCTION halting all [Product] sales. FINAL DEMAND This is [Patent Owner]'s final demand before commencing federal court litigation. Within ten (10) days, [Defendant] must: 1. Confirm in writing that all manufacture, sale, and marketing of [Product] has ceased; 2. Provide complete accounting of [Product] sales since [Date of Prior Notice]; 3. Propose compensation for past infringement. If we do not receive a satisfactory response by [Deadline Date], we will file a complaint for patent infringement in the [U.S. District Court for the _____ District of _____] without further notice. We will seek all available remedies including enhanced damages for willful infringement. This matter could have been resolved amicably. [Defendant]'s refusal to engage has made litigation necessary. Very truly yours, [Attorney Name] [Firm Name] Counsel for [Patent Owner] cc: [Patent Owner]
Defenses & Responding to Patent Demands
Received a Patent Demand? Don't panic, but don't ignore it. Patent demands require careful analysis because they can lead to expensive litigation—but many claims are weak or overstated.
Initial Assessment
  • Verify patent status: Check USPTO Patent Center—is patent expired, lapsed for non-payment of maintenance fees, or subject to ongoing IPR/reexam?
  • Identify claims at issue: Which specific claims are allegedly infringed? Request claim chart if not provided
  • Analyze ownership: Does sender actually own or have standing to enforce the patent?
  • Review prosecution history: Did claims get narrowed during prosecution? Estoppel may limit scope
  • Search for prior art: Was relevant prior art missed? Could support invalidity defense
Common Patent Defenses
Defense Legal Basis When It Applies
Non-Infringement 35 U.S.C. § 271 Accused product is missing at least one claim element; no literal or DOE infringement
Invalidity – Anticipation 35 U.S.C. § 102 Prior art reference discloses every element of claim before priority date
Invalidity – Obviousness 35 U.S.C. § 103 Combination of prior art references would make claimed invention obvious to POSITA
Invalidity – Written Description 35 U.S.C. § 112 Patent specification doesn't adequately describe claimed invention
Invalidity – Enablement 35 U.S.C. § 112 Patent doesn't teach how to make/use invention without undue experimentation
Exhaustion First sale doctrine Patent rights exhausted by authorized sale—resellers/users can't be liable
License/Authorized Use Express or implied You have license rights (purchased from licensee, industry standard, etc.)
Inequitable Conduct Fraud on USPTO Patent procured through fraud—renders patent unenforceable (rare, hard to prove)
Prosecution History Estoppel Claim narrowing DOE doesn't cover subject matter surrendered during prosecution
Response Options

1. Design-Around:

  • Modify product to remove one or more claim elements
  • Fastest, cheapest option if technically feasible
  • Document the design-around in case of later dispute

2. Take a License:

  • If patent is valid and infringed, licensing may be cheaper than litigation
  • Negotiate reasonable royalty rate; request most-favored-licensee clause
  • Consider cross-licensing if you have relevant patents

3. Challenge Validity (IPR/PGR):

  • File Inter Partes Review (IPR) at USPTO within 1 year of suit
  • Lower burden (preponderance vs. clear and convincing) than court
  • Often used to invalidate weak patents or as leverage for settlement

4. Declaratory Judgment Action:

  • Sue patent owner for declaration of non-infringement/invalidity
  • Choose your preferred forum; go on offense
  • Requires "case or controversy"—demand letter usually sufficient

5. Ignore (Risky):

  • Letter creates actual notice—willfulness clock starts
  • If they sue, silence can be used against you
  • Generally not recommended unless letter is clearly baseless
Opinion of Counsel: Historically, obtaining a written opinion from patent counsel showing non-infringement or invalidity could negate willfulness. Post-Halo, this is less critical but still valuable for showing good-faith belief.
Red Flags in Patent Demands
  • No claim chart: Serious patent owners do the analysis; vague accusations suggest fishing
  • Overly broad claims: Demand covers obviously non-infringing products
  • Expired or lapsed patent: Check maintenance fee status
  • Prior art visible on face: Product predates patent? Patent may be invalid
  • Mass mailing: Same letter to hundreds of targets suggests low-quality enforcement
  • No real product: NPE/PAE may have weaker case on damages; less injunction threat
Attorney Services for Patent Disputes
Patent Enforcement or Defense?

I represent patent owners seeking to monetize their innovations and businesses defending against infringement claims. Whether you need to enforce your patent rights or respond to a demand letter, I provide strategic counsel focused on efficient resolution.

For Patent Owners
  • Analyze patents and products for infringement
  • Prepare claim charts demonstrating infringement
  • Draft cease-and-desist and demand letters
  • Negotiate licensing agreements and settlements
  • File patent infringement lawsuits in federal court
  • Seek preliminary and permanent injunctions
  • Pursue ITC Section 337 exclusion orders for imports
  • Coordinate with foreign counsel for international enforcement
For Accused Infringers
  • Analyze validity and infringement of asserted patents
  • Prepare non-infringement and invalidity opinions
  • Respond to demand letters with substantive defenses
  • Negotiate licenses on favorable terms
  • File IPR/PGR petitions at USPTO to invalidate weak patents
  • Defend patent litigation in federal court
  • File declaratory judgment actions in favorable forums
  • Design-around counseling to avoid infringement
Why Patent Disputes Require Specialized Counsel
Technical Complexity: Patent disputes require understanding both the technology and the law. Claim construction, infringement analysis, and validity challenges demand experience with patent prosecution, litigation, and the relevant technical field. I work with technical experts to build strong cases.
Cost Considerations
  • Demand letters: Often resolve disputes for a fraction of litigation cost
  • IPR: $15,000-$40,000 USPTO filing fee; typically $100,000-$300,000 total
  • District court litigation: $500,000-$3,000,000+ through trial
  • Licensing: Running royalty of 1-5% is common; depends on industry and patent scope
Schedule a Call

Book a call to discuss your patent matter. I'll review the patent(s), assess infringement or validity, and recommend a strategy for enforcement or defense.

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Generate a professional demand letter, CA court complaint, or arbitration demand

Contact Information

Email: owner@terms.law

Frequently Asked Questions
Federal patent litigation typically takes 2-4 years from filing to trial. Key stages include: claim construction hearing (Markman hearing) at 12-18 months, discovery lasting 12-18 months, summary judgment motions, and trial. Many cases settle after claim construction, when both sides better understand their positions. The Eastern District of Texas, Western District of Texas, and District of Delaware have specialized patent dockets. IPR proceedings at USPTO take about 18 months.
Reasonable royalties vary widely by industry and patent scope. Courts use the Georgia-Pacific factors (15 factors) to determine royalties in litigation. Common ranges: pharmaceutical 5-20%, consumer electronics 1-5%, software 1-3%, manufacturing 2-5%. The royalty should reflect what a willing licensor and licensee would agree to in a hypothetical negotiation. Comparable licenses for the same patent or similar technology are strong evidence.
Generally no. The doctrine of patent exhaustion means that when a patented product is sold with the patent owner's authorization, the patent rights in that particular item are "exhausted." Buyers can use, resell, or modify the product without infringing. However, if the product was made without authorization (e.g., counterfeit or unauthorized import), or if you're using a licensed product outside the scope of the license, you could potentially face liability.
IPR is a proceeding at the USPTO's Patent Trial and Appeal Board (PTAB) to challenge the validity of patent claims based on prior art (patents and printed publications). It must be filed within one year of being sued for infringement. IPR uses a lower burden of proof (preponderance) than district court (clear and convincing evidence), making it easier to invalidate patents. The process takes about 18 months and costs $100,000-$300,000. IPR is often used as leverage in licensing negotiations.
Patent Damages Calculator

Estimate potential damages for patent infringement claims under 35 U.S.C. Section 284. This calculator provides rough estimates based on reasonable royalty and lost profits theories.

Estimated Patent Damages

Reasonable Royalty: $0
Lost Profits: $0
Base Damages (higher of royalty or profits): $0
Enhanced Damages (willfulness multiplier): $0
Attorney Fees (if exceptional case): $0
Adjusted for Patent Strength: $0
Estimated Total Recovery Range: $0
Disclaimer: This calculator provides rough estimates for educational purposes only. Actual patent damages depend on complex legal analysis including claim construction, Georgia-Pacific factors, Panduit test for lost profits, and case-specific facts. Enhanced damages require proof of willfulness under Halo v. Pulse. Consult a patent attorney for accurate damage assessments.