Recent scholarship in just war theory has challenged the principle of symmetrical application of International Humanitarian Law (IHL). This revisionist work, which is increasingly dominating the field of contemporary war ethics, rejects the idea that the rules of conduct of war ( jus in bello ) should be agnostic about the justice of the decision to go to war ( jus ad bellum ). Just wars are perceived to be inherently at odds with the principle of symmetrical application of IHL, which appears to create a hard choice between justice and legality. I show that this challenge to IHL is misplaced. It derives from a widespread view among just war theorists according to which only one side in a just war can be justified in using force. By looking closely at the nature of adjudication of just causes of war, I show that there can be cases of war in which both sides are justified in using force, and cases in which, though not objectively justified, both sides may be excused for fighting. On the basis of this understanding of jus ad bellum , I argue that the principle of symmetrical application of IHL in fact best reflects the uncertainty and complexity that should characterize the practical doctrine of jus ad bellum .