Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd.

Summary

Justice Kennedy delivered the unanimous opinion holding that a narrowing amendment made to satisfy any requirement of the Patent Act may give rise to prosecution history estoppel, including an amendment addressing § 112. The Court rejected the Federal Circuit’s complete bar against equivalents for an amended claim element. Instead, a narrowing amendment presumptively surrenders the territory between the original and amended claims, but the patentee may show that the particular equivalent was not surrendered because it was unforeseeable, was only tangentially related to the amendment’s rationale, or could not reasonably have been described for another reason. The Court vacated and remanded for consideration of whether Festo could overcome that presumption. There were no separate opinions.