Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co.,
535 U.S. 722 (2002)

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No. 00-1543. Argued January 8, 2002-Decided May 28, 2002

Petitioner Festo Corporation owns two patents for an industrial device.

When the patent examiner rejected the initial application for the first patent because of defects in description, 35 U. S. C. § 112, the application was amended to add the new limitations that the device would contain a pair of one-way sealing rings and that its outer sleeve would be made of a magnetizable material. The second patent was also amended during a reexamination proceeding to add the sealing rings limitation. After Festo began selling its device, respondents (hereinafter SMC) entered the market with a similar device that uses one two-way sealing ring and a nonmagnetizable sleeve. Festo filed suit, claiming that SMC's device is so similar that it infringes Festo's patents under the doctrine of equivalents. The District Court ruled for Festo, rejecting SMC's argument that the prosecution history estopped Festo from saying that SMC's device is equivalent. A Federal Circuit panel initially affirmed, but this Court granted certiorari, vacated, and remanded in light of Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U. S. 17,29, which had acknowledged that competitors may rely on the prosecution history to estop the patentee from recapturing subject matter surrendered by amendment as a condition of obtaining the patent. On remand, the en banc Federal Circuit reversed, holding that prosecution history estoppel applied. The court ruled that estoppel arises from any amendment that narrows a claim to comply with the Patent Act, not only from amendments made to avoid the prior art, as the District Court had held. The Federal Circuit also held that, when estoppel applies, it bars any claim of equivalence for the element that was amended. The court acknowledged that, under its prior cases, prosecution history estoppel constituted a flexible bar, foreclosing some, but not all, claims of equivalence, depending on the purpose of the amendment and the alterations in the text. However, the court overruled its precedents on the ground that their case-by-case approach had proved unworkable.

Held: Prosecution history estoppel may apply to any claim amendment made to satisfy the Patent Act's requirements, not just to amendments made to avoid the prior art, but estoppel need not bar suit against every equivalent to the amended claim element. Pp.730-742.


(a) To enable a patent holder to know what he owns, and the public to know what he does not, the inventor must describe his work in "full, clear, concise, and exact terms." § 112. However, patent claim language may not describe with complete precision the range of an invention's novelty. If patents were always interpreted by their literal terms, their value would be greatly diminished. Insubstantial substitutes for certain elements could defeat the patent, and its value to inventors could be destroyed by simple acts of copying. Thus, a patent's scope is not limited to its literal terms, but embraces all equivalents to the claims described. See Winans v. Denmead, 15 How. 330, 347. Nevertheless, because it may be difficult to determine what is, or is not, an equivalent, competitors may be deterred from engaging in legitimate manufactures outside the patent's limits, or lulled into developing competing products that the patent secures, thereby prompting wasteful litigation. Each time the Court has considered the doctrine of equivalents, it has acknowledged this uncertainty as the price of ensuring the appropriate incentives for innovation, and it has affirmed the doctrine over dissents that urged a more certain rule. See, e. g., id., at 343, 347. Most recently, Warner-Jenkinson, supra, at 28, reaffirmed the doctrine. Pp. 730-733.

(b) Prosecution history estoppel requires that patent claims be interpreted in light of the proceedings before the Patent and Trademark Office (PTO). When the patentee originally claimed the subject matter alleged to infringe but then narrowed the claim in response to a rejection, he may not argue that the surrendered territory comprised an unforeseen equivalent. See Exhibit Supply Co. v. Ace Patents Corp., 315 U. S. 126, 136-137. The rejection indicates that the patent examiner does not believe the original claim could be patented. While the patentee has the right to appeal, his decision to forgo an appeal and submit an amended claim is taken as a concession that the invention as patented does not reach as far as the original claim. See, e. g., Goodyear Dental Vulcanite Co. v. Davis, 102 U. S. 222, 228. Were it otherwise, the inventor might avoid the PTO's gatekeeping role and seek to recapture in an infringement action the very subject matter surrendered as a condition of receiving the patent. pp. 733-735.

(c) Prosecution history estoppel is not limited to amendments intended to narrow the patented invention's subject matter, e. g., to avoid prior art, but may apply to a narrowing amendment made to satisfy any Patent Act requirement, including § 112's requirements concerning the patent application's form. In Warner-Jenkinson, the Court made clear that estoppel applies to amendments made for a "substantial reason related to patentability," 520 U. S., at 33, but did not purport to catalog every reason that might raise an estoppel. Indeed, it stated that even

Full Text of Opinion

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