[eng] Environmental law principles are one of the relevant threads of the legal tapestry underpinning many of the claims and judicial decisions examined in this book. Although a relatively recent category of norms, such principles, developed mainly over the last 40 years, have acquired an increasingly relevant role in the definition and progression of environmental law. In this chapter, we will start by analysing the emergence, content and legal scope of these principles, examining how they have come to shape, if not always the content, at least the boundaries of the negotiating framework of most of the relevant international environmental law instruments, including the climate change regime. In a second section, we will then examine to what extent those principles have influenced the current trend of domestic climate change litigation, providing a detailed analysis of the use of environmental principles in recent cases.