The chief means to limit and calculate the costs of war are the philosophical and legal concepts of proportionality and necessity. Both categories are meant to restrain the most horrific potential of war. The volume explores the moral and legal issues in the modern law of war in three major categories. In so doing, the contributions will look for new and innovative approaches to understanding the process of weighing lives implicit in all theories of jus in bello: who counts in war, understanding proportionality, and weighing lives in asymmetric conflicts. These questions arise on multiple levels and require interdisciplinary consideration of both philosophical and legal themes.