What is a patent troll?
A patent troll is a company whose main business is asserting patents rather than using them. It usually doesn't make or sell anything. Instead it acquires patents, often broad ones from failed startups or old portfolios, and then sends letters or files lawsuits demanding license fees from businesses that it says are infringing. Researchers and regulators prefer neutral terms like patent assertion entity (PAE) or non-practicing entity (NPE).
Not every non-practicing patent owner is a troll. Universities, independent inventors and research labs also license patents they don't commercialize. The label usually points to a business model built on the cost of defense: if fighting a suit costs a defendant millions, a demand for a smaller sum looks cheap even when the claim is weak.
- Business model
- License fees and settlements
- Typical targets
- Small businesses, retailers, app makers
- Main tools
- Demand letters and infringement suits
- Key defenses
- Non-infringement, invalidity, IPR
A patent is a right to exclude. Patent trolls turn it into a right to collect, from people who often never saw the patent.
How the demand letter strategy works
Many campaigns start with a demand letter sent to hundreds of businesses at once. A well-known example in the early 2010s targeted small offices for using ordinary scan-to-email features on office equipment. Letters typically claim infringement in general terms, propose a per-employee license fee and set a short deadline.
Because the letter often comes from a shell company, targets can't easily see who owns the patent or how many others received the same demand. In 2016 the Federal Trade Commission published a study of PAE activity and found that most licenses won by litigation-focused PAEs were worth less than $300,000, roughly the cost of defending a patent suit through its early stages. That is the core of the model. Since Vermont passed the first law in 2013, more than thirty states have enacted statutes against bad-faith patent demand letters.
U.S. cases and reforms that changed the game
Several Supreme Court decisions and a major statute reduced trolls' leverage.
- eBay v. MercExchange (2006)
- No automatic injunction; courts apply four equitable factors
- Alice v. CLS Bank (2014)
- Abstract ideas implemented on a computer aren't patentable
- Octane Fitness (2014)
- Easier fee awards in exceptional cases
- TC Heartland (2017)
- Suits against U.S. companies must be filed where they're incorporated or have a regular place of business
eBay Inc. v. MercExchange, 547 U.S. 388 (2006), mattered because the threat of an injunction shutting down a product line gave patent holders huge bargaining power. After eBay, a patent owner that doesn't make products usually gets money damages, not an order to stop. Alice made many broad software and business-method patents vulnerable, and TC Heartland cut down filings in the Eastern District of Texas, which had been a favorite venue.
The America Invents Act of 2011 created inter partes review (IPR) at the Patent Trial and Appeal Board, a faster and cheaper way to challenge a patent's validity using prior patents and publications. Defendants now routinely file IPR petitions alongside litigation.
Korea's approach
Korea sees fewer troll suits than the U.S., but Korean exporters are frequent targets abroad, and domestic letters do happen. The main tools are administrative trials at the Intellectual Property Trial and Appeal Board: an invalidation trial (Patent Act art. 133) to cancel a patent, and a scope-confirmation trial (art. 135) to confirm a product falls outside a patent's claims.
In courts, the Supreme Court held in an en banc decision in 2012 (2010Da95390) that suing on a patent with an obvious ground for invalidity is an abuse of rights, even before the patent is formally invalidated. Korea also raised damages for willful infringement, first to up to three times actual damages in 2019 and then to five times in 2024, which helps real innovators but can also raise the stakes of troll claims. Litigation basics are in civil procedure steps.
A Korean report on Responding to Patent Troll Demand Letters, Font Copyright Claims and Trademark Infringement: Four IP Disputes Small Korean Companies Face walks through these defenses alongside font copyright and trademark claims, and a paper on Copyright for Applied Art and Characters in Korea: Supreme Court Case 2015Do11550, Separability, and U.S., German and Japanese Comparisons covers a related IP question about character designs.
| United States | Korea | |
|---|---|---|
| Validity challenge | Inter partes review (PTAB) | Invalidation trial (art. 133) |
| Scope question | Claim construction in court | Scope-confirmation trial (art. 135) |
| Injunctions | Four-factor test (eBay) | Generally available; abuse-of-rights limit |
| Bad-faith letters | State statutes, FTC | General civil and competition law |
What to do if you get a patent demand letter
- Don't ignore it, and don't pay right away. Note the deadline and keep every document.
- Identify the patent and owner. Look up the patent number, check whether it's expired, and search for other suits by the same owner.
- Compare the claims. Infringement requires every element of a claim, so read the claims, not just the abstract.
- Check validity. Look for prior art, and consider whether the patent claims an abstract idea.
- Ask your vendor. If the accused feature comes from software or equipment you bought, the seller may owe you indemnity.
- Get advice. Many patent attorneys offer short consultations, and some trade groups track known campaigns.
This is general information, not legal advice. Businesses also face other IP claims, such as copyright notices over images or fonts; see copyright basics for the differences.
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Criticism and debate
Critics argue trolls tax innovation, drain small businesses and clog courts with weak claims. Defenders reply that PAEs give individual inventors and small firms a way to monetize patents against large companies that might otherwise ignore them, and that the real problem is low-quality patents, not who owns them. Some economists also question how much reform has helped, since trolls adapted by filing in new venues. The debate overlaps with broader questions in consumer protection about deceptive letters aimed at people who can't evaluate them.
The best defense often starts before any letter arrives. Knowing your vendors, your licenses and your products' features turns a scary letter into a checklist.
- What is a patent troll in simple terms?
- It's a company that makes money by threatening patent lawsuits instead of making products, hoping targets will pay to avoid the cost of fighting.
- Is being a patent troll illegal?
- No. Owning and enforcing patents is legal, but sending deceptive bad-faith demand letters is restricted by many state laws, and weak suits can lead to fee awards.
- Should I pay a patent demand letter?
- Not before checking the patent, comparing its claims to your product and getting advice, because many demands are weak or based on invalid patents.
References and official sources
- eBay Inc. v. MercExchange, L.L.C., 547 U.S. 388 (2006). Justia
- Alice Corp. v. CLS Bank Int'l, 573 U.S. 208 (2014). Justia
- Patent Assertion Entity Activity: An FTC Study (2016). FTC
- Patent troll, Wex. Cornell LII
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