What exactly is it we wage when we wage war? This is the crucial question addressed in this largely rewritten edition of the author's classic text. The range of possible answers to it has already framed much of the ethical discourse that can be conducted about war, as well as about other uses of force. Only when some of those fundamental issues have been clarified can we then safely foray into the dense ethical thicket that surrounds this topic. The book shows how recent developments in warfare, particularly related to new technologies and asymmetries, have disturbed traditional paradigms.