Scientific advisory committees (SACs) are a critically important part of international environmental policy  First, SACs play a critical role in agenda setting. Second, the effectivenss of a given SAC and the associated regime is variable. Third, there is variations in the extent to which the regime is driven by an overarching scientific consensus. Fourth, the role of science varies with the nature of the problem facing the regime. Finally, the cases examoned suggest that the institutional design of the SACs matter and can influence the overall effectiveness of the regime but it is seldom decisive.