This book investigates how sustainability informs key principles and concepts of domestic and international law. It calls for the recognition of ecological sustainability as a fundamental principle to guide the entire legal system rather than just environmental legislation. To this end, the book makes a contribution to global environmental constitutionalism, a rapidly growing area within comparative and international environmental law and constitutional law. This 2nd edition has been fully revised and updated to take account of recent developments and new case law. The book will be a valuable resource for students, researchers and policy makers working in the areas of environmental law and governance.