Th is book is the result of a long process. Fresh water has for many years been a topic of profound interest to me in the course of my activities as an academic and practitioner. Studying the treatment of fresh water in international law makes one aware of the complexity involved in the law’s protection and management of this natural resource, and of the way in which diff erent bodies of science (earth sciences, hydrology, engineering, meteorology, agronomy, and others) exert their infl uence on it. International law is an important tool in this respect but even its role cannot be defi ned in the singular. Indeed, various bodies of norms are applicable and have left their mark on the role and modalities of international law as regards fresh water: territorial and boundary regimes, economic law, environmental law, human rights, law of international organizations, etc. Th e real issue is the consistency and the coherence in the interpretation and application of these sets of norms. A variety of methods and techniques should give eff ect to them, allowing each to be applied in recognition of the vital nature of water for humans and the environment. Th e approach adopted in this book is to analyse the origin and scope of the various bodies of international norms, while emphasizing their interconnectedness and necessary adaptation to one another. Th is approach is accompanied by a detailed analysis of the practice of States and of international organizations, all the while taking into account the activities of the many non-State actors involved in the area of fresh water.