On January 20, 2015, the Supreme Court issued its long-awaited decision on the standard of review of factual findings by the trial court in construing patent claims. The Court ruled that factual findings in the context of claim construction are subject to Rule 52(a)(6) of the Federal Rules of Civil Procedure, which sets out a deferential “clearly erroneous” standard of review on appeal. The Court thus established two standards of review for claim construction rulings: “clearly erroneous” review of factual findings based on extrinsic evidence, and de novo review for legal findings, including the meaning of the intrinsic evidence (the claims, specification, and file wrapper) and “the ultimate question of proper construction of the patent.” Teva Pharmaceuticals USA, Inc., et al. v. Sandoz, Inc., et al., 574 U.S. ___ (2015).

The Supreme Court granted certiorari in the Teva Pharmaceuticals case to review the Federal Circuit’s rule that findings of fact in claim construction are subject to the stricter de novo review standard. Teva Pharmaceuticals had sued Sandoz Inc. and others for infringement after they applied for pre - market approval from the FDA of generic versions of a Teva - produced drug for treating multiple sclerosis. Sandoz argued to the trial court that a particular claim term – “molecular weight” – was subject to three different interpretations and thus was invalid for indefiniteness. Both parties presented expert evidence regarding what an ordinary artisan would have understood “molecular weight” to mean at the time of the invention. The District Court found Teva’s expert more compelling, and rejected Sandoz’s indefiniteness argument. On appeal, the Federal Circuit, applying the de novo standard of review, determined that Sandoz’s experts were mo re credible, and that the “molecular weight” term was indefinite because it was subject to multiple interpretations. Teva applied for a writ of certiorari on the basis that the Federal Circuit applied the wrong standard for reviewing the trial court’s factual findings.