This book explores the conditions under which Nuclear Weapons Free Zones (NWFZs) can be established. It analyses four hypotheses that explain the factors contributing to the formation of NWFZs, building upon realist, constructivist, and liberal theories from International Relations. Via the method of structured focused comparison, the book presents and compares the emergence of NWFZs in Latin America, the South Pacific, Southeast Asia, Africa, Central Asia, and the Middle East, which is a prospect of NWFZ. The book argues that NWFZ projects depend on the following conditions: the security interest of regional states in avoiding nuclear threats; pre-existing regional institutions and regional economic interdependence; leadership by a core of regional powers and normative context. Democracy is not a necessary condition, but the democratization process can help overcome barriers presented by hesitant or opposed regional governments. This book will be of much interest to students of nuclear proliferation, arms control, security studies and International Relations.