The essays chosen for this rich volume are an attempt by its editors to “unsettle” the legacy and understanding of the bombing of Hiroshima, an act that triggered the nuclear age 75 years ago. This collection explores the age’s unanswered questions from a global perspective, rather than through the prism of the Cold War. It is not only geographically broad; it is also enriched by the diverse perspectives of historians, political scientists, and other theorists of international relations. One set of chapters reveals, for example, that the familiar binary categories of nuclear state and nonnuclear state hide a fluid spectrum of conditions of which these are merely the endpoints. Other chapters explore the ways political and cultural contexts constrain the choices leaders can make about nuclear weapons and programs. And some contributors wrestle with the surprising fact that many pivotal questions about the nuclear age—for instance, does deterrence work?—remain unanswerable.