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File history estoppel is, like the doctrine of equivalents, an equitable doctrine developed over the years by the federal judiciary in its consideration of patent infringement cases. File history estoppel prevents patent owners from alleging infringement (either directly or under the doctrine of equivalents) on the basis of an unclaimed element, or elements, of a patented invention, where the allegedly infringed element(s) were surrendered during patent prosecution.

The Doctrine of Equivalents is an equitable, common law, judge-made principle developed by the Federal Courts over years of litigation. This article explores some of the key cases that have defined and re-defined the Doctrine of Equivalents, including Winans v. Denmead (1853), Graver Tank & Mfg. Co. v. Linde Air Products (1950), and Warner-Jenkinson Co. v. Hilton Davis Chemical Co. (1997).