In Cybor Corp. v. FAS Techs., Inc., 138 F.3d 1448 (Fed. Cir. 1998), the Federal Circuit ruled that it would review the construction of claim terms in patent cases on appeal without deference to the ruling of the district court because claim construction is a pure legal conclusion for which no deference to the district court is appropriate. Many commentators, however, have long criticized the decision in Cybor because there are often factual determinations underlying a district court’s decision on claim construction, such as how people skilled in the technology at issue would understand a particular claim term. According to the commentators, the district court hears this evidence and so is best situated to assess that evidence and make these determinations. The commentators also believe that the Cybor decision has led to an increase by the Federal Circuit in reversing claim construction rulings of district courts. As a result, parties sometimes incur great expense litigating a case under one claim construction, only to have to re-try the case after the Federal Circuit changes the claim construction on appeal. Recently, the Federal Circuit agreed to review its previous Cybor decision en banc, asking the parties in Lighting Ballast Control v. Phillips Elecs. N. Am. Corp., Nos. 2012-1014, -1015 (Fed. Cir. Mar. 15, 2013), to present arguments as to whether the Federal Circuit should overrule Cybor and afford deference to a district court’s claim construction and, if so, to identify the aspects of the district court’s ruling that should be afforded deference. The parties’ briefing will be complete by mid-June 2013, after which the en banc Federal Circuit will hear oral argument.