This chapter focuses on the intricate relationship between sustainable development, the environment, and international investment within the framework of IIL over the past fifty years. It begins by tracing the evolution of IIL and clarifying its core purpose, which is to provide investment protection commitments as outlined in BITs. Next, the chapter shifts its focus to the diverse concerns of signatories of IIAs that extend beyond the mere protection of investments. It highlights the crucial role of sustainable development and emphasises the necessity of environmental protection as an essential component of development in the context of IIA negotiations. This background sets the stage for a comprehensive discussion on the importance of preserving policy space within IIAs. Building on this foundation, the chapter also explores new proposals regarding the right to regulate in the context of IIA negotiations. Additionally, it conducts an in-depth review of treaties that include investment protection commitments, with special attention given to the CPTPP, the USMCA, and the AfCFTA.