This chapter examines the rules relating to marine scientific research as they apply to marine geoengineering taking place in areas beyond national jurisdiction (ABNJ). It analyses the regime currently evolving under the 1996 London Protocol to the 1972 London (Dumping) Convention, which has been developed to manage ocean fertilization scientific research in the context of the regulation of marine scientific research under the 1982 United Nations Convention on the Law of the Sea (UNCLOS). As the Southern Ocean has been the location for several ocean fertilization experiments to date, the relevant rules under the 1991 Environmental Protocol to the 1959 Antarctic Treaty, particularly environmental impact assessments, will also be assessed. The chapter briefly assesses the relationship between these regimes and the future Agreement under UNCLOS on the conservation and sustainable use of biodiversity and concludes that this Agreement—whatever the outcome of the negotiations—will not operate as a panacea for managing activities in ABNJ. With respect to geoengineering marine scientific research, the paper argues that the potential ‘solution’ to managing its risks lies in supporting and implementing the existing regime.