Effective measures to tackle the adverse effects of anthropogenic damage to the environment require continuous cooperation between multiple stakeholders and at all governmental echelons, from local to national to regional and global (the latter two requiring intergovernmental arrangements), representing a wide variety of interests. Designing, adopting, implementing, monitoring, and enforcing these measures require sound (i.e., best available, accurate, and objective) and sustained scientific input throughout the entire regulatory process governing the activities at all levels. Optimal deployment of this essential input improves formulation and application of measures best suited to achieve the environmental objectives sought. Achieving effective scientific involvement is particularly challenging at the global intergovernmental level. In the environmental domain, under the auspices of a variety of intergovernmental bodies, countries endeavor to cast environmental measures in the form of legally binding global regulatory instruments. Many factors contribute to creating a constructive setting in which to elaborate these instruments. Addressed here are: (1) the institutional framework to support effective scientific involvement, and (2) the associated methodology. Both are needed to identify, obtain, and present sound science to the decision-makers responsible for developing and approving these measures. This chapter offers institutional and methodological suggestions to enhance the utility of the scientific input presented to decision-makers, illustrated by examples from the Office of the London Convention and Protocol and the International Seabed Authority, intergovernmental bodies regulating marine geoengineering and seabed mining, respectively. It contributes to implementing scientific aspects of environmental protection requirements of the 1982 United Nations Convention on the Law of the Sea, with particular attention to those set out in its Article 243.