What is the doctrine of equivalents actually testing?
Whether the difference between a claim limitation and the corresponding part of the accused product or process is insubstantial. The Supreme Court in Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605 (1950), sustained a finding of equivalence where manganese silicate was substituted for magnesium silicate in a welding flux, and described the inquiry in terms that survived into modern practice: whether the substitute performs substantially the same function in substantially the same way to obtain the same result.
Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997), declined to make that formulation the exclusive test. The Court said the particular linguistic framework used is less important than whether the test is probative of the essential inquiry — whether the accused product or process contains elements identical or equivalent to each claimed element — and noted that function-way-result may suit mechanical devices while providing a poor framework for other products and processes. Graver Tank also directs attention to whether a person reasonably skilled in the art would have known of the interchangeability of the substituted ingredient, which is why the evidence that carries this issue is usually contemporaneous technical literature rather than an expert’s present-day judgment.
Does the doctrine of equivalents apply to the invention as a whole?
No. Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997), held that each element in a claim is deemed material to defining the scope of the patented invention, so the doctrine of equivalents must be applied to individual elements of the claim rather than to the invention as a whole. This is the all-elements rule, and it means an equivalents case is built limitation by limitation in the same structure as a literal case, not as an argument that two things are broadly alike.
Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997), also supplied the limit that gets argued about. The Court said it is important to ensure that the application of the doctrine, even as to an individual element, is not allowed such broad play as to effectively eliminate that element in its entirety, which is where the vitiation argument comes from. The Federal Circuit narrowed how that argument can be used in Deere & Co. v. Bush Hog, LLC, 703 F.3d 1349 (Fed. Cir. 2012), holding that vitiation is not an exception to the doctrine of equivalents but a legal determination that no reasonable jury could find two elements equivalent, and that the vitiation test cannot be satisfied by simply noting that an element is missing from the claimed structure or process, because the doctrine of equivalents by definition recognizes that an element is missing and must be supplied by an equivalent substitute. Deere & Co. v. Bush Hog, LLC vacated summary judgment of no infringement under the doctrine of equivalents on that reasoning.
When does prosecution history estoppel bar the doctrine of equivalents, and what is the Festo presumption?
Estoppel arises where an applicant narrowed claim scope during prosecution to obtain the patent, and Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002), held that a narrowing amendment made to satisfy any requirement of the Patent Act — not only an amendment made to avoid prior art — may give rise to it. The Court rejected a complete bar in favor of a presumption: the patentee is presumed to have surrendered the territory between the original claim and the amended one, and bears the burden of showing that the amendment did not surrender the particular equivalent at issue.
Festo identified three routes for rebutting the presumption: that the equivalent was unforeseeable at the time of the amendment, that the rationale underlying the amendment bore no more than a tangential relation to the equivalent in question, or that there was some other reason suggesting the patentee could not reasonably have been expected to describe the insubstantial substitute. On remand, Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 344 F.3d 1359 (Fed. Cir. 2003) (en banc), held that rebuttal is a question of law for the court rather than a jury question, and that narrowing is a prerequisite — if the amendment was not narrowing, prosecution history estoppel does not apply. Warner-Jenkinson supplies the rule for a silent record: where the reason for a narrowing amendment cannot be established, the court should presume the Patent Office had a substantial reason related to patentability.
Can estoppel arise from something other than an amendment to the asserted claim?
Yes, in at least two ways, and both are easy to miss when only the amendments are reviewed. The first is argument-based estoppel. In Amgen Inc. v. Coherus BioSciences, Inc., 931 F.3d 1154 (Fed. Cir. 2019), the Federal Circuit affirmed dismissal of an equivalents claim because during prosecution the applicant had clearly and unmistakably surrendered salt combinations other than the particular combinations recited in the claims, in arguments responding to an obviousness rejection. Statements to an examiner can foreclose scope even where no claim language changed.
The second is cancellation of a related claim. In Colibri Heart Valve LLC v. Medtronic CoreValve, LLC (Fed. Cir. July 18, 2025), the applicant had prosecuted two independent claims reciting partial deployment of a replacement heart valve — one by pushing, one by retracting a sheath — and canceled the retracting claim after the examiner rejected it for lack of written description under 35 U.S.C. section 112. The Federal Circuit held that the required narrowing is not a purely formal matter of altering a single claim’s terms, and can exist substantively where canceling a closely related claim involving such intertwined terminology that the cancellation necessarily communicated that the scope of the retained claim had narrowed. Holding the equivalents theory barred, the Federal Circuit reversed the district court’s denial of judgment as a matter of law of noninfringement on a jury verdict of more than $106 million.
What is the disclosure-dedication rule?
Subject matter that a patent discloses but does not claim is dedicated to the public and cannot be recaptured through the doctrine of equivalents. The Federal Circuit adopted that rule en banc in Johnson & Johnston Associates Inc. v. R.E. Service Co., 285 F.3d 1046 (Fed. Cir. 2002), stating that when a patent drafter discloses but declines to claim subject matter, that action dedicates the unclaimed subject matter to the public, and reasoning that recapturing it under equivalents would conflict with the primacy of the claims in defining the patentee’s exclusive right.
It is an independent bar, and it operates alongside estoppel rather than as an alternative to it. In Actelion Pharmaceuticals Ltd. v. Mylan Pharmaceuticals Inc., No. 2024-1641 (Fed. Cir. May 13, 2026), a panel of Judges Reyna, Taranto and Stoll affirmed a judgment of noninfringement under the doctrine of equivalents on both grounds: prosecution history estoppel, because the applicant narrowed a pH limitation in response to an obviousness rejection and failed to show the amendment was only tangential to the alleged equivalent, and, independently, the disclosure-dedication rule, because the specification disclosed pH ranges below the claimed threshold that the asserted claims did not recite. The practical point for anyone reading a specification before asserting equivalents is that a generous disclosure of alternatives is also a list of things that cannot be reached by equivalence.
When should a party decide whether it has a real equivalents case?
Before the theory is written into contentions, because the material that decides it — the file wrapper, the specification, and what was said to the examiner — exists already and does not change. Every one of the limits described here is established from the intrinsic record, and under Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 344 F.3d 1359 (Fed. Cir. 2003) (en banc), the estoppel questions are for the court, which means they can be resolved on summary judgment or on judgment as a matter of law rather than by a jury that heard the technical story sympathetically.
That is also why an equivalents theory is worth stating limitation by limitation and testing against the record for each one, in the same discipline described in what makes a claim chart actually prove infringement, and why it has to be squared with the prior art the way a literal construction does in why claim construction decides the case. Nothing here is an opinion on whether any particular patent is infringed or valid; that is the expert analysis the infringement proof area of this Institute exists to support. What a finding would be worth is a separate question, and the royalty and apportionment machinery belongs to our Economic Damages Institute.