The importance of identifying, preserving and protecting marine biological diversity (biodiversity) has been a growing theme in the last 20 years. Given UNCLOS centrality, pre-eminence and comprehensiveness, all other specific conventions that apply to the marine environment such as those that pertain to specific uses of the sea (eg shipping) or to the conservation of specific ecosystems, habitats or species (eg for wetlands of international importance) should be seen as putting into operation the principles and provisions of UNCLOS. The first part of this chapter analyses the provisions in UNCLOS that seek to protect and preserve marine biodiversity in light of international case law. The second and third parts discuss legally adopted scientific criteria to identify ecosystems, habitats or species that should be protected as a matter of priority. The final part discusses the protection of marine biodiversity in areas beyond national jurisdiction.