This Handbook is the definitive volume on the state of international security and the academic field of security studies. It provides a tour of the most innovative and exciting news areas of research as well as major developments in established lines of inquiry. It presents a comprehensive portrait of an exciting field, with a distinctively forward-looking theme, focusing on the question: what does it mean to think about the future of international security? The key assumption underpinning this volume is that all scholarly claims about international security, both normative and positive, have implications for the future. By examining international security to extract implications for the future, the volume provides clarity about the real meaning and practical implications for those involved in this field. Yet, contributions to this volume are not exclusively forecasts or prognostications, and the volume reflects the fact that, within the field of security studies, there are diverse views on how to think about the future. Readers will find in this volume some of the most influential mainstream (positivist) voices in the field of international security as well as some of the best known scholars representing various branches of critical thinking about security. The topics covered in the range from conventional international security themes such as arms control, alliances and Great Power politics, to "new security" issues such as global health, the roles of non-state actors, cyber-security, and the power of visual representations in international security. The is a twelve-volume set of reference books offering authoritative and innovative engagements with the principal sub-fields of International Relations. The series as a whole is under the General Editorship of Christian Reus-Smit of the University of Queensland and Duncan Snidal of the University of Oxford, with each volume edited by specialists in the field. The series both surveys the broad terrain of International Relations scholarship and reshapes it, pushing each sub-field in challenging new directions. Following the example of Reus-Smit and Snidal's original , each volume is organized around a strong central thematic by scholars drawn from different perspectives, reading its sub-field in an entirely new way, and pushing scholarship in challenging new directions.