Asymmetric conflict is changing the way that we practice and think about war. Torture, rendition, assassination, blackmail, extortion, direct attacks on civilians, and chemical weapons are all finding their way to the battlefield despite long-standing prohibitions. This book offers a practical guide for policymakers, military officers, lawyers, students, journalists and others who ask how to adapt the laws and conventions of war to the changing demands of asymmetric conflict. As war wages between state and nonstate parties, difficult questions arise about the status of guerrillas, the methods each side may use to disable the other and the means necessary to identify and protect civilians caught in the crossfire. Answering these questions while providing each side a reasonable chance to press its claims by force of arms requires us to reevaluate the principle of noncombatant immunity, adjust the standards of proportionality, and redefine the limits of unnecessary suffering and superfluous injury. In doing so, many practices that conventional war prohibits are slowly evolving into new norms of asymmetric conflict.