This Essay considers the role of international legal argument in the war on terror and, in particular, in the attempts to justify the use of military force. Part I looks at challenges posed by the evolution of military conflict and how this affects diplomacy. In particular, I argue that a reputation for honoring one's treaty commitments and for legality, more generally, is an important part of fostering cooperation and undercutting the support of our adversaries. Part II focuses on how the Bush Administration moved between hostility to international law and attempts to rewrite the rules of international law concerning the use of force. Finally, Part III considers some of the effects of these legal policies on U.S. foreign policy.