On each occasion that public international law is tested – be it its goals or how it is conceived, orchestrated and applied by a variety of societal actors – fundamental socio-legal questions arise. This is because this legal framework is often seen as more than just a neutral body of norms that purports to regulate the relations between States and other entities – or between these other entities themselves. Instead, it is perceived as having in itself some blueprint for improving the world, or those aspects where it operates. In a context in which those participating within the international realm offer different means to achieve the goals that this regime has (or intends to have), this book explores the legal regulation of non-State armed groups’ detention activities in non-international armed conflicts.