This Article discusses the appellate standard of review of claim constructions. The recent decision by the US Court of Appeals for the Federal Circuit in Lighting Ballast Control LLC v. Philips Electronics North America Corp. upheld the decision in Cybor Corp. v. FAS Techs., Inc. that a district court’s claim construction is given no deference on appeal. However, the US Supreme Court recently granted a petition for certiorari in Teva Pharm. USA, Inc. v. Sandoz, Inc. and will consider whether to maintain this de novo review standard.