This book provides a comprehensive yet concise overview of key issues related to the regulation of armed hostilities between States, and between States and non-State groups. Coverage begins with an explanation of the conditions that result in the applicability of international humanitarian law, and then subsequently addresses how the law influences a broad range of operational, humanitarian, and accountability issues that arise during military operations. Each chapter provides a clear and comprehensive explanation of humanitarian law, focusing especially on how it impacts operations. The chapters also highlight both contemporary controversies in the field and potentially emerging norms of the law. The book is an ideal text for students studying international humanitarian law for the first time, as well as an excellent introduction for students and practitioners of public international law and international relations.