What Does a Patent Notice Letter Actually Require? Understanding ‘Actual Notice’

Imagine an inventor creates an implement that they wish to mass produce and sell. Perhaps they do not want to patent it for some reason, or perhaps they believe the implement to be within the public domain, but regardless they do not believe themselves to be infringing on any existing patent rights. Years and years go by and they are very successful in their business, making many sales over time. However, one day they are suddenly served with a lawsuit alleging that they have been infringing on someone else’s patent rights all along, and that this plaintiff is seeking damages for every unit ever sold.

Were the plaintiff to prevail, the resulting damages would be immense, and the situation would feel inequitable, especially since the infringer was acting in good faith and had no reason to believe that they were doing anything wrong. Nonetheless, direct patent infringement is strict liability, and the defendant does not need to know they were doing anything wrong to be held liable. However, allowing the accumulation of pre-suit damages to reach back to before the infringer was put on notice of the patent holder’s rights could also have the absurd result of incentivizing the patentee to delay their enforcement action as long as possible, so that they can seek damages for a greater number of infringing units. In order to eliminate this sort of ensnarement behavior and to prevent innocent individuals from being held liable while acting in good faith, the patent statute requires that patent owners put would-be infringers on notice of their intellectual property rights before they are able to hold them liable for any acts of infringement. But what does a notice letter need for it to count? How granular must it be? Are claim charts required?

What the Statute Says

Section 287(a) of the Patent Act is titled ‘Limitation on damages and other remedies; marking and notice’ and says that: “Patentees, and persons making, offering for sale, or selling within the United States any patented article for or under them […] may give notice to the public that the same is patented.” They can do so by providing constructive notice through markings on the patented implements that they sell. Section 287 also permits patentees to provide actual notice, such as through so-called ‘notice letters’ whereby the patentee or their agent sends a letter to notify an identified infringer. The relevant section of the statute relays: “In the event of failure so to mark, no damages shall be recovered by the patentee in any action for infringement, except on proof that the infringer was notified of the infringement and continued to infringe thereafter, in which event damages may be recovered only for infringement occurring after such notice. Filing of an action for infringement shall constitute such notice.” The U.S. Court of Appeals for the Federal Circuit has read this as putting the burden of providing sufficient notice on the patentee, without regard for the perception of the infringer. The court stated: “It is irrelevant [under § 287] … whether the defendant knew of the patent or knew of his own infringement. The correct approach to determining notice under [§] 287 must focus on the action of the patentee, not the knowledge or understanding of the infringer.” Amsted Indus. Inc. v. Buckeye Steel Castings Co., 24 F.3d 178, 187 (Fed. Cir. 1994).

The statute, however, does not dictate exactly what a notice letter must contain to be considered sufficient to provide actual notice. For that, we need to look at Federal Circuit case law and the doctrine that it has developed over the past few decades. In Amsted, a patent holder had sent multiple companies an identical form letter indicating that they had acquired several patents that they intended to enforce, that the recipients should acquaint themselves with those patents, and that they should refrain from infringing on the rights that they provide. The letter did not identify the defendant in particular, did not accuse them of infringement explicitly, and did not indicate the patent which was believed to be infringed. For the court, this letter was too vague, as “[a]ctual notice requires the affirmative communication of a specific charge of infringement by a specific accused product or device.” Id. That is to say, actual notice requires that specific parties be put on clear notice of what rights they are allegedly violating and what conduct of theirs is at issue.

Federal Circuit Case Law

SRI Int’l Inc. v. Adv. Tech. Lab’ys Inc., 127 F.3d 1462 (Fed. Cir. 1997) further solidified the Federal Circuit’s position in Amsted and clarified what a ‘specific charge’ entails. In SRI, the infringer argued that the notice letter was defective, as it offered a potential licensing agreement rather than threatening a lawsuit. In their view, this did not level an unqualified charge of infringement, nor did it create an actual controversy, and as such it should not satisfy the requirements for actual notice under § 287(a). The court, however, rejected this argument and found the notice effective, holding that “the actual notice requirement of § 287(a) is satisfied when the recipient is informed of the identity of the patent and the activity that is believed to be an infringement, accompanied by a proposal to abate the infringement, whether by license or otherwise.” Id. at 1470. This slight broadening provided a greater amount of flexibility for patent holders, as they could now comfortably seek licenses without worrying that they were forgoing a period of the damages window by not threatening immediate litigation.

Two later decisions mildly expanded the scope of what was considered to provide actual notice. Standing in tension with the patentee’s burden of providing sufficient notice to infringers, both of these cases allowed for actual notice to reach beyond the specific products mentioned in the notice letters at issue. First, in Gart v. Logitech, 254 F.3d 1334 (Fed. Cir. 2001), the court allowed for two subsequent letters to be considered sufficient actual notice of infringement, despite that, when read individually, they would be insufficient. In this case the defendant sold two products, both of which contained similar electrical components. In 1995 they were sent a notice letter indicating an allegation of infringement of a specific patent by one of the defendant’s products and given an offer to purchase a license. The court found this notice to be sufficient. Then in 1996, another letter was sent regarding the same patent, but this time it mentioned both products when suggesting that the defendant avoid infringing that patent. The defendant argued that since the 1996 letter was incomplete in relation to the second product, it did not provide actual notice. The court held that while “standing alone, this letter would not constitute effective actual notice,” (Id. at 1346) since it was not the first communication, it could be read in conjunction with the 1995 letter and thus could provide actual notice of infringement by the second product.

Then, in Funai Elec. Co., Ltd. v. Daewoo Elecs. Corp., 616 F.3d 1357 (Fed. Cir. 2010), the Federal Circuit went one step further, holding that while specificity as to the infringing product is required for actual notice, “when the threshold specificity is met, the ensuing discovery of other models and related products may bring those products within the scope of the notice.” Id. at 1373. In this case, notice letters and claim charts were provided which were undisputed to provide actual notice of infringement by the two product models mentioned. However, the defendant argued that the letter was legally insufficient to provide actual notice as to any other models, thus seeking to limit the period of damages as to those models. Considering the technical similarities between all of the models, the Court rejected the argument that the defendant lacked actual notice of their infringement, and as such held that the letters and charts sent were sufficient to provide actual notice of infringement for all like models. So long as the theory of infringement is materially the same, a notice letter as to one model can extend to another.

The Federal Circuit most recently addressed the marking statute in August 2026 in VDPP, LLC v. Volkswagen Grp. of Am., Inc., No. 2024-2226, 2026 WL 2416565 (Fed. Cir. Aug. 19, 2026). That case re-stated more forcefully what had already been assumed in prior cases: The marking statute applies to licensees just as much as patent owners, and makes no distinction between non-practicing entity (NPE) patent owners versus practicing patent owners.  If a licensee makes a product covered by an apparatus claim of an NPE’s patent, the licensee’s failure to mark will cut off the NPE’s past damages up until the point where the current defendant is notified of the infringement claim.  But because the patent owner in VDPP had not sent notice letters before suing, the question of what is required to make a notice letter sufficient was not presented.

What the District Courts Have Said

While the Federal Circuit has not expressly addressed whether the notice letter must include claim charts that explain the infringement allegations on a limitation-by-limitation basis, some district courts have. Though reversed on grounds not relevant here, the Court in the Southern District of New York in SIMO Holdings Inc. v. Hong Kong uCloudlink Network Tech. Ltd., 376 F. Supp.3d 369 (S.D.N.Y. 2019), expressly rejected that claim charts are required to provide actual notice to infringers, stating “the Federal Circuit has never required anything nearly so detailed.” This same sentiment is echoed by the Court in the Eastern District of Michigan in Lear Corp. v. NHK Seating of Am. Inc., 2022 WL 870834 (E.D. Mich. Mar. 23, 2022). In that case, the Court found the notice letter to be sufficient when some patents had related claim charts while others did not. Further, they did not find that the notice was retracted when further claim charts for the other patents were not given. On the other hand, in the Eastern District of Wisconsin in Acantha LLC v. Depuy Orthopaedics Inc., 2018 WL 1951231 (E.D. Wis. Apr. 2018), held that “general letters referring to the patent and including an admonishment not to infringe do not constitute actual notice,” but that providing representative claim charts asserting that the products were covered by the patent’s claims was sufficient. But then that part of Acantha was vacated by the same court. 2019 WL 6710913 (E.D. Wis. Oct. 8, 2019). Accordingly, while claim charts may be sufficient for providing actual notice to infringers, they are not required in order to do so.

In the Eastern District of Texas, a hotbed of patent infringement lawsuits, the issue of whether patent notice letters must include claim charts has not yet been directly addressed. In cases regarding similar issues to the ones faced by the district courts mentioned above, Magistrate Judge Payne has recommended denial of defendants’ motion for summary judgment on alleged lack of actual notice, and has never granted it in any other matter. For example, Judge Payne has addressed issues of whether a group of products can be identified rather than individual devices in Optis Wireless Tech., LLC v. Apple, 2:19-cv-00066, ECF 142 (E.D. Tex. July 2018), and denied Apple’s summary judgment motion on the issue.  But no case before him has squarely presented the question of whether a notice letter was sufficient in situations where there was no claim chart included, or other public information such as industry standards from which the accused infringer could understand the allegations.

The Future of Marking

While the doctrine underlying patent notice letters has some strong anchor points, it has the potential to continue to grow and develop over time, especially as the positions of various districts become more settled. That being said, it is an area that is worth keeping an eye on in the near future, especially as it relates to non-practicing patent owners who license to manufacturers who will not agree to mark or who fail to do so, thus forcing the patentee to provide actual notice to infringers to comply with Section 287(a)’s marking requirements.

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