Understanding the global security environment and delivering the necessary governance responses is a central challenge of the 21st century. On a global scale, the central regulatory tool for such responses is public international law. But what is the state, role, and relevance of public international law in today’s complex and highly dynamic global security environment? Which concepts of security are anchored in international law? How is the global security environment shaping international law, and how is international law in turn influencing other normative frameworks? The Oxford Handbook of the International Law of Global Security provides a ground-breaking overview of the relationship between international law and global security. It constitutes a comprehensive and systematic mapping of the various sub-fields of international law dealing with global security challenges, and offers authoritative guidance on key trends and debates around the relationship between public international law and global security governance. This Handbook highlights the central role of public international law in an effective global security architecture and, in doing so, addresses some of the most pressing legal and policy challenges of our time. The Handbook features original contributions by leading scholars and practitioners from a wide range of professional and disciplinary backgrounds, reflecting the fluidity of the concept of global security and the diversity of scholarship in this area.