Based on an innovative theory of international law, Janina Dill's book investigates the effectiveness of international humanitarian law (IHL) in regulating the conduct of warfare. Through a comprehensive examination of the IHL defining a legitimate target of attack, Dill reveals a controversy among legal and military professionals about the 'logic' according to which belligerents ought to balance humanitarian and military imperatives: the logics of sufficiency or efficiency. Law prescribes the former, but increased recourse to IHL in US air warfare has led to targeting in accordance with the logic of efficiency. The logic of sufficiency is morally less problematic, yet neither logic satisfies contemporary expectations of effective IHL or legitimate warfare. Those expectations demand that hostilities follow a logic of liability, which proves impracticable. This book proposes changes to international law, but concludes that according to widely shared normative beliefs on the twenty-first-century battlefield there are no truly legitimate targets.