This essay defends the constitutional validity of the Military Order issued by President Bush on November 13, 2001, which authorizes the establishment of military commissions to try certain non-citizens involved in terrorism. The essay begins by describing the ways in which military commissions have been used throughout U.S. history. It then explains why President Bush had statutory authority to issue the Military Order, and why he probably also had independent constitutional authority to do so as Commander in Chief. Although the Order was not preceded by a congressional declaration of war, the essay argues that such a declaration is not constitutionally required in order for the President to exercise his constitutional or statutory war powers, including his power to establish military commissions. Finally, the essay argues that the September 11 terrorist attacks, to which the Order was a response, violate the laws of war and therefore fall within the jurisdiction of military commissions.