This chapter assesses war and intervention. Just war theorists share two beliefs: that wars can, at least in theory, sometimes be just, and that the fighting of war is governed by moral rules. Just war theory is usually divided into jus ad bellum, jus in bello, and jus post bellum. Jus ad bellum (justice prior to war) sets the conditions under which it is just to declare war. Jus in bello (justice during the war) sets the ‘rules of engagement’, governing the conduct of combatants during a conflict. Jus post bellum (justice after war) deals with topics like war reparations and punishment of aggression and had, until recently, received comparatively little attention in the just war literature. Meanwhile, pacifism and realism offer alternative approaches to the ethics of war.