In Festo, (Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 234 F.3d 558 (Fed. Cir. 2000)), the Federal Circuit essentially eliminated application of the Doctrine of Equivalents to elements of claims that have been amended in prosecution before the U.S. Patent and Trademark Office ("PTO").
By way of review; a patent claim is infringed only if all elements recited in the claim are found either literally or by equivalents in the accused infringing product or process. The Doctrine of Equivalents is generally applied to determine whether a particular element, not found literally in the accused product or process, is present in some equivalent form such that the accused infringer should still be held liable. A variety of tests have been defined by the Federal Circuit for determining whether an aspect of the accused product or process is equivalent to corresponding recited elements in the patent claim at issue. The Supreme Court has held in Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997) that "prosecution history estoppel" may limit the application of the Doctrine of Equivalents. Prosecution history estoppel is an equitable doctrine that estops a patent holder from asserting a scope of protection for a claim that has been surrendered in the "prosecution history" before the PTO. The prosecution history is, in essence, all communications between the patent holder (applicant) and the PTO during the pendency of the patent at issue. The Supreme Court held in Warner that such prosecution history estoppel may limit or completely bar application of the Doctrine of Equivalents to those elements of a patent claim affected by such prosecution history.
In Festo, the Federal Circuit found that a number of issues relating to application of the Doctrine of Equivalents remain unsettled by the Supreme Court's decision in Warner. Specifically in Festo, the Federal Circuit rules on four questions - namely:
For the purposes of determining whether an amendment to a claim creates prosecution history estoppel, is "a substantial reason related to patentability," Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 33, 117 S. Ct. 1040, 137 L. Ed. 2d 146 (1997), limited to those amendments made to overcome prior art under ? 102 and ? 103, or does "patentability" mean any reason affecting the issuance of a patent?
Under Warner-Jenkinson, should a "voluntary" claim amendment - one not required by the examiner or made in response to a rejection by...