In October 2012, a panel of the D.C. Circuit dealt a blow to the United States’ post- September 11, 2001 decade-long experiment with military commissions as a forum for trying Guantanamo Bay detainees. Specifically, the court concluded that prior to the 2006 statutory reforms, military commission jurisdiction was limited to violations of internationally-recognized war crimes; that providing material support to terrorism was not an internationally-recognized war crime; and that the military commission conviction of Salim Hamdan for material support charges based on pre-2006 conduct was therefore invalid. Three months later, a panel of the D.C. Circuit reached the same conclusion with respect to conspiracy and solicitation charges, and vacated the conviction and life sentence of Guantanamo Bay detainee Ali Hamza Ahmad al Bahlul. That case is now on appeal to an en banc (full court) panel of the D.C. Circuit. This article analyses the D.C. Circuit’s ruling in Hamdan’s case, explaining why the ultimate holding is the right one, even though some of the reasoning is flawed, and why the ruling should be upheld on appeal. It also highlights the many unresolved questions and the implications for the future of military commissions at Guantanamo Bay. As the article explains, the D.C. Circuit’s rulings are a major victory for the rule of law and a major defeat for commissions.