There has been a long, intellectual tradition in thinking about the moral justification of war, ranging at least from Thomas Aquinas’s writings in the 13th century to Michael Walzer’s instant classic, Just and Unjust Wars. The contemporary advent of terrorism arguably challenges central tenets of the just war tradition, replacing the doctrine of preemption with that of prevention, blurring the distinction between civilians and combatants, accelerating both the speed and potential damage of attacks, and so on. How, if at all, should these features of terrorism lead to a revision of just war principles?