The issue of protecting marine species is a matter that falls within the interface of the international law of the sea and international environmental law. It is thus characterized by the concurrence and overlap of different legal traditions and underlying interests. There has been considerable evolution in the nature of instruments and strategies, but this evolution has been governed in a de-centralized and fragmented manner, and it has been influenced by a plethora of different actors. Improvements in scientific knowledge as well as societal considerations have further increased the complexity of regulation. Different scales and types of protection strategies have emerged, ranging from those addressing individual species and species habitats to those that treat species protection as a component of the broader categories of biodiversity and ecosystem-based management and, finally, to science-driven precautionary measures that proactively regulate potentially adverse impacts on species, habitats, food webs and ecosystems. This chapter examines the complex legal regime for the protection of marine species by focusing on the issue from two angles: First, it examines the approaches taken in the law of the sea. It then turns to an examination of the approaches that have been included in several multilateral environmental agreements. The chapter concludes with some comments on the interrelationship of these two regimes and the need to ensure their complementary interaction.