This introduction points to the challenge of sustainable development being ushered as an overarching objective of international law and policy, and a recalibrating principle of the international investment regime, while also having a disputed legal nature. In this paradox lies the justification of this study. The reader is introduced to each of the different contributions to solving this paradox under the chapters of the book. The discussion on sustainable development and international investment law is framed within broader considerations on structural transformations of international law in the context of globalization, thus highlighting the global, transnational nature of sustainable development.