War and law seem to occupy different worlds, but this powerful work by a Harvard legal scholar probes the modern transformation of warfare and the growing "merger" of the "professional vernaculars" of military force and law. In the traditional view, war and peace are sharply divided realms: peace ends when a state declares war, at which point law gives way to emergency powers. Kennedy argues that beginning with the Cold War and continuing with the rise of low-intensity conflict and the "war on terror," the distinction between war and peace has broken down. At the same time, ideas about law and military conduct are changing: international law has increasingly taken the form of humanitarian and human rights norms, while military establishments are increasingly infused with bureaucratic legal guidance. Kennedy's interesting claim is that these complex developments have turned war into a "legal institution" in which the use of force is governed by a dense network of rules and shared assumptions among global elites. Many people applaud this legal-professional turn in modern warfare, but Kennedy worries that the language of law has in fact diffused responsibility and eroded political leadership in the wielding of violence. This is an original contribution to the debate about the perils of liberal democracy in an age of limited but unending war.