File Wrapper Estoppel Law and Legal Definition

File wrapper estoppel is also known as prosecution history estoppel. According to U.S. patent law, file wrapper estoppel means to indicate that a party making amends to a patent application after filing the application cannot have a cause of action for infringement of pre-amendment patent claims.

The following are the two types of file wrapper estoppel:

1. Amendment Estoppel;

2. Argument Estoppel.

File wrapper estoppel essentially means that when an inventor during prosecution narrows down his/her invention to escape prior art by some amendment, s/he cannot claim that someone else infringed his/her patent under the doctrine of equivalence. The doctrine of file wrapper estoppel was developed in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 128 S. Ct. 2903 (U.S. 2008).