The book describes and analyses how environmental issues are regulated in several federal, regional and unitary systems and in the European Union. The comparative analysis reveals common trends towards a multi-layered environmental governance, cross-cutting traditional distinctions among different state models. In the second part, the case study of the management and protection of water resources is selected and analysed in the same legal systems. Disaggregating environmental protection into more specific competence fields allows trends and challenges to be tested. The book casts light on the relationship between the state models as to the division of powers and environmental governance. It develops theoretical and practical foundations of contemporary, multi-level environmental law and challenges consolidated approaches in federal studies.