On Friday, the Court of Appeals for the Federal Circuit ordered en banc review to address long-standing questions regarding the standard of review for claim construction in patent cases. In Lighting Ballast Control LLC v. Philips Electronics North America Corp. et al., Nos. 2012-1014, -1015 (Fed. Cir. Mar. 15, 2013), the Court granted plaintiff Lighting Ballast’s petition for rehearing en banc. This case may lead to fundamental, far-reaching changes in patent law and patent litigation strategies.

The core issue under review is whether the Federal Circuit should afford any deference to district court rulings on claim construction. The Federal Circuit has long held that construing the claim terms of a patent presents a pure question of law, which is therefore subject to de novo review on appeal with no deference to a district court’s conclusions. Specifically, in Cybor Corp. v. FAS Technologies, Inc., the full Court held that, “as a purely legal question, we review claim construction de novo on appeal including any allegedly fact-based questions relating to claim construction.” 138 F.3d 1448, 1456 (Fed. Cir. 1998) (en banc). Critics of this rule have noted that district courts must often resolve highly factual issues to construe patent claims (such as weighing the credibility of experts), and that de novo review has contributed to a high reversal rate of claim construction rulings by the Federal Circuit.

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