Legal Definitions - file-wrapper estoppel

Definition: File-wrapper estoppel is a legal principle that limits a patent holder's ability to claim infringementbased on the doctrine of equivalents. It arises from the prosecution history of a patent, which is the record of communications between the patent applicant and the patent office during the process of obtaining the patent.

Example: Suppose a patent application claims a device with a certain feature, but the patent office rejects the claim as too broad. The applicant then amends the claim to exclude the feature and the patent is granted. Later, the patent holder sues a competitor for infringement, arguing that the competitor's device is equivalent to the patented device. The competitor could argue that the patent holder is estopped from making this claim because they surrendered the feature during the prosecution of the patent.

Explanation: This example illustrates how file-wrapper estoppel can limit a patent holder's ability to assert infringement based on the doctrine of equivalents. By amending the claim to exclude the feature, the patent holder effectively disclaimed it and cannot later argue that the competitor's device infringes based on that feature. This principle helps to ensure that patents are granted only for what is actually invented and claimed, rather than for broader concepts that are later asserted through the doctrine of equivalents.