The main theme of this volume of the Yearbook of International Humanitarian Lawis the development and interpretation of international humanitarian law (IHL). It iselaborated upon in several chapters that examine the role of non-state armed groupsin the development and interpretation of IHL, the impact of international criminal lawon the development of IHL, the notion of external non-international armed conflicts,and the regulation of prolonged occupation under international law. The second theme of this volume is dedicated to targeting in armed conflicts. Specifictopics include precautions in attack in urban and siege warfare, the targeting of theIslamic State’s religious personnel in Iraq and Syria, and the targeting of illicit cropsthrough aerial spraying in Colombia. Besides the chapters that address both themes,this volume also contains a Year in Review describing the most important events andlegal developments that took place in 2017. The Yearbook of International Humanitarian Law is the world’s only annual publicationdevoted to the study of the laws governing armed conflict. It provides a truly internationalforum for high-quality, peer-reviewed academic articles focusing on this crucialbranch of international law. Distinguished by contemporary relevance, the Yearbookof International Humanitarian Law bridges the gap between theory and practice andserves as a useful reference tool for scholars, practitioners, military personnel, civilservants, diplomats, human rights workers and students.