War is not the only or even the major cause of human suffering. But it is the cause for which we are most often most directly responsible. Our voluntary choices result in huge increases in mortality, massive refugee crises, and the dislocation of whole generations. So while there are other equally pressing problems facing humanity, none of them raises as pointed moral questions as those to do with whether and when we may take our polities to war and how we must fight if we do so. This Handbook offers a guide to thinking through the morality of war, from the perspective of contemporary analytical just war theory. This introduction explains the methodological and substantive choices made in designing the volume, then summarizes the key insights of the chapters to follow.