The general introduction sets the scene for the legal issues addressed in this book by presenting their relevance in most recent conflicts and other situations of violence, including in Syria, Iraq, Libya, Ukraine, the Central African Republic, and Kenya. It also introduces the legal framework the book sets out to examine, notably international humanitarian law, human rights law, and international criminal law. The introductory chapter further presents the book’s methodology, introduces its structure, and explains key terms and concepts. These include, in particular, the terms ‘non-state armed group’, ‘international legal personality’, and ‘degree of organization’, which are especially relevant throughout the book.