Claim construction plays a central role in nearly every patent litigation. It is also critical to patent prosecution, patent licensing, and cumulative innovation by delineating the scope of patent protection and the opportunity to work around patent boundaries. Yet since the Supreme Court’s 1996 Markman decision, the Federal Circuit has struggled to articulate a consistently reproducible methodology for construing the scope of patent claims, resulting in high reversal rates and consternation among the federal judiciary, litigants, and patent prosecutors. Using a comprehensive, granular, hand-coded database of all Federal Circuit decisions between 2000 and 2011, we examine the evolution and current status of claim construction jurisprudence. We find that immediately after the Federal Circuit’s 2005 en banc decision in Phillips v. AWH Corp., the claim construction reversal rate dropped precipitously and has remained substantially below the pre-Phillips levels. We explore several competing hypotheses to explain this drop and conclude that the most plausible explanation was a shift away from de novo review and towards a more deferential review of claim construction decisions. The paper also reports several other patterns in claim construction jurisprudence.