Background
Festo Corporation owned two patents on an improved magnetic rodless cylinder — a piston-driven device that uses magnets to move objects through industrial conveying systems. The device found uses in sewing equipment, amusement park rides, and countless other manufacturing applications. During prosecution of both patents, Festo had narrowed claim elements to comply with the Patent Act. After Festo began marketing its device, SMC Corporation entered the market with a competing product that differed in two respects: it used one two-way sealing ring instead of two one-way rings, and it used a nonmagnetizable sleeve material.
Festo sued SMC for infringement under the doctrine of equivalents — the legal doctrine that allows a patent to be infringed by a device that does not literally fall within the claims but achieves substantially the same function, in substantially the same way, to achieve substantially the same result. SMC countered with prosecution history estoppel, arguing that because Festo had narrowed its claims during prosecution, Festo was “estopped” — legally barred — from asserting equivalents for the amended elements.
The district court found infringement under the doctrine of equivalents. The Federal Circuit initially affirmed, but then took the case en banc to reconsider the scope of prosecution history estoppel.
The Court’s Holding
The Federal Circuit en banc majority adopted a sweeping “complete bar” rule: whenever a patent applicant narrows a claim during prosecution to comply with the Patent Act — whether to avoid prior art, to satisfy § 112 written description or enablement requirements, or for any other patentability reason — estoppel arises and completely bars any later claim of equivalence for the amended element. No equivalents. No exceptions. The complete bar applied regardless of whether the specific equivalent in question was actually the reason the amendment was made.
The majority justified the complete bar on grounds of certainty: the doctrine of equivalents had generated uncertainty in patent scope, and a bright-line rule would make it easier for competitors to know what was and was not covered by a patent. The majority overruled more than fifty of its own prior decisions that had applied a more flexible, case-by-case approach to prosecution history estoppel.
Four judges dissented vigorously. Judge Michel’s dissent catalogued the majority’s overruling of eight older Federal Circuit decisions and noted that the complete bar would unsettle the expectations of patentees who had relied on the prior flexible-bar framework. Other dissenters argued that the complete bar was inconsistent with the Supreme Court’s prior decision in Warner-Jenkinson Co. v. Hilton Davis Chemical Co. (1997), which had preserved prosecution history estoppel as a limitation on — but not a complete elimination of — the doctrine of equivalents.
Key Takeaways
- The en banc Federal Circuit adopted a complete-bar rule: any narrowing amendment during prosecution bars all equivalents claims for the amended element, with no exceptions.
- The rule applied regardless of the reason for the narrowing amendment — whether to overcome prior art, satisfy written description requirements, or any other ground.
- The decision overruled more than fifty Federal Circuit precedents applying a flexible prosecution history estoppel standard.
- The Supreme Court vacated this decision in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002), holding that narrowing amendments create a rebuttable presumption of surrender, not an absolute bar — and identifying three ways a patentee can rebut the presumption.
- Together, the Federal Circuit’s complete bar and the Supreme Court’s flexible bar define the ongoing scope of prosecution history estoppel doctrine.
Why It Matters
Festo is one of the most consequential — and controversial — Federal Circuit decisions in patent history. The complete bar rule, had it stood, would have fundamentally constrained the doctrine of equivalents: any claim amendment would have permanently eliminated equivalents protection for the amended element, no matter how loosely related the amendment was to the equivalent at issue. Patent prosecutors would have faced an impossible dilemma: amend to get the patent granted, or preserve equivalents by refusing to amend.
The Supreme Court’s unanimous reversal preserved a workable middle ground. A narrowing amendment now raises a presumption that the patentee surrendered the equivalent in question — but the patentee can rebut that presumption by showing the equivalent was unforeseeable at the time of amendment, the rationale for the amendment bore only a tangential relation to the equivalent, or some other reason suggests the patentee could not reasonably have been expected to claim the substitute. The Federal Circuit’s en banc Festo decision thus lives on as a cautionary benchmark — and as the starting point for understanding the prosecution history estoppel doctrine that governs patent infringement analysis today.