War is about individuals maiming and killing each other, and yet, it seems that it is also irreducibly collective, as it is fought by groups of people and more often than not for the sake of communal values such as territorial integrity and national self-determination. Cécile Fabre articulates and defends an ethical account of war in which the individual, as a moral and rational agent, is the fundamental focus for concern and respect--both as a combatant whose acts of killing need justifying and as a non-combatant whose suffering also needs justifying. She takes as her starting point a political morality to which the individual, rather than the nation-state, is central, namely cosmopolitanism. According to cosmopolitanism, individuals all matter equally, irrespective of their membership in this or that political community. Traditional war ethics already accepts this principle, since it holds that unarmed civilians are illegitimate targets even though they belong to the enemy community. However, although the traditional account of whom we may kill in wars is broadly faithful to that principle, the traditional account of why we may kill and of who may kill is not. Cosmopolitan theorists, for their part, do not address the ethical issues raised by war in any depth. Fabre's Cosmopolitan War seeks to fill this gap, and defends its account of just and unjust wars by addressing the ethics of different kinds of war: wars of national defence, wars over scarce resources, civil wars, humanitarian intervention, wars involving private military forces, and asymmetrical wars.