It is well-established law that the meaning of claim terms ("claim construction") is to be determined by a judge, even when such determination requires consideration of factual evidence. To date, all claim construction rulings have been reviewed de novo (i.e., without any deference to the district court's findings). However, the Supreme Court recently decided in Teva Pharmaceuticals USA, Inc. v. Sandoz, Inc., et al. (January 20, 2015) that in order to overturn a district judge's resolution of an underlying factual dispute in a claim construction analysis, clear error must be found.
The case at hand involved a Teva patent for a drug, which it asserted was infringed by several generic manufacturer defendants. The district court determined, after hearing from experts on both sides, that a particular claim term asserted to be indefinite was not. Under its long-standing precedents, the Federal Circuit reviewed the claim construction analysis de novo, including testimony from the parties' experts, and found that the claim term was indefinite.
In Teva, the Supreme Court held that the Federal Circuit must apply the "clear error" standard of review with respect to the factual determinations, but made it clear that claim constructions, without such determinations, are still to be reviewed de novo on appeal. Given that claim construction rulings often do not involve factual determinations, it remains to be seen how widely this decision will impact future cases. In any event, it is important to consider this decision when presenting your claim construction analysis, as well as in making a decision as to whether to pursue an appeal on a claim construction ruling.