The obligation to conduct environmental impact assessment (EIA) of activities with the potential for significant impact on the marine environment within and beyond national jurisdiction has attained customary international law status. The related but broader process of strategic environmental assessment (SEA) is also applied to plans, policies and programmes with the potential for significant impact on the marine environment in many national jurisdictions and in a transboundary context. The application of EIA and SEA for activities with the potential for significant impact on marine areas beyond national jurisdiction (ABNJ) has been much more ad hoc. This commentary reviews the initiatives being taken by the international community to develop a more comprehensive legal and institutional framework for EIA and SEA of activities affecting ABNJ. It examines the role of sectoral environmental assessment in ABNJ, as well as the potential role of global guidelines for EIA and SEA of activities affecting ABNJ.