Marine resources in areas beyond national jurisdiction (ABNJ) are under increasing pressure from human impacts, putting at risk biodiversity, ecosystem processes and function. There is a heightened focus on whether current arrangements and policies are adequate. This paper explores possible elements of a new instrument to protect such biodiversity an Implementation Agreement under the United Nations Convention on the Law of the Sea (UNCLOS). As the fourth element in the Marine Series, it should be read in conjunction with the other three.