'Overall, the book is a great source for anyone interested in the general theoretical issues of customary international law, as well as those who have an interest in narrower questions on the role that international organisations and non-state actors have at different stages of the making of customary international law.' Journal of International Law of Peace and Armed Conflict'The book is a great source for anyone interested in the general theoretical issues of customary international law, as well as those who have an interest in narrower questions on the role that international organisations and non-state actors have at different stages of the making of customary international law. Outside of theory, the volume offers the reader an opportunity to look at the theoretical issues from a practical perspective.' Humanitäres Völkerrecht