Patent Amendments and Prosecution History Estoppel Under Festo

On November 29, 2000, the Federal Circuit retroactively reduced the value of nearly 1.2 million unexpired United States patents by announcing a new rule for the somewhat obscure doctrine of prosecution history estoppel. Designed to foster clarity in patent applications, this new pronouncement in Festo Corp v. Shoketsu Kinzoku Kogyo Kabushiki Co. allows for easy copying of some patented inventions and reduces patent owner's ability to prove infringement. This article outlines the change in the law and discusses the positive and negative consequences of the decision.