415 F.3d 1303 (Fed. Cir. 2005) (en banc)
Phillips v. AWH Corp.
How should courts properly construe patent claim terms—specifically, whether the term "baffles" should be limited to angled, projectile-deflecting structures based on the specification—and, more generally, what evidentiary sources and hierarchy govern claim construction?
Claim terms are given their ordinary and customary meaning as understood by a person of ordinary skill in the art at the time of the invention, read in the context of the entire patent. The intrinsic record—the claims, the specification, and the prosecution history—is the primary and most reliable guide to meaning. The specification is usually the best source for understanding claim scope, but courts must not import limitations from embodiments into the claims absent clear language, express definitions (lexicography), or unmistakable disavowal. Prosecution history may inform the meaning and limit scope through clear and unmistakable disclaimer. Extrinsic evidence, including dictionaries and expert testimony, may be considered to educate the court but carries less weight and cannot contradict the intrinsic record. Claim differentiation may support broader readings but is a guide, not an absolute rule. At the time of Phillips, claim construction was treated as a question of law reviewed de novo on appeal.
The Federal Circuit (en banc) held that intrinsic evidence, especially the specification, is the primary guide to claim meaning and rejected approaches that give dictionaries primacy. Applying that framework, the court concluded that the term "baffles" was not limited to structures oriented at acute angles solely to deflect projectiles; nothing in the claims or specification clearly required that limitation, and the presence of dependent claims specifying angular ranges counseled against reading such a restriction into the independent claims. The court vacated the judgment of noninfringement and remanded for further proceedings under the proper construction.
Phillips is the definitive framework for claim construction: it reaffirms the primacy of intrinsic evidence and cabins the use of dictionaries and other extrinsic materials. It harmonizes earlier cases, curbing the Texas Digital approach that prioritized dictionary definitions, and clarifies when and how to read limitations from the specification (rarely) and how claim differentiation, lexicography, and prosecution disclaimer operate. For law students, it is essential to understanding how courts translate technical patent language into enforceable rights and how drafting and prosecution choices affect scope. The case also anchors later developments, including Supreme Court decisions on the standard of review for subsidiary factual findings in claim construction.