The contribution of international institutions to the reduction of uncertainties which prevent that states can manage trans-boundary environmental problems effectively has been referred to as one among a number of grounds which justify obedience. Uncertainties can occur in many different ways. Special attention will be given to uncertainties in the cognitive setting. Cognitive factors can influence the evolution of state preferences and regime policies. Functional regime theory or knowledgebased approaches emphasize the role of institutions for the reduction of transaction costs, for raising concern for trans-boundary problems, for the development of new policies, or for capacity-building (Keohane 1984; Levy, Keohane and Haas 1993). These conceptions of regimes are based on the assumption that preferences of self-interested actors are not fix but can be influenced by a changing knowledgebase or by rising incentives provided by a regime to participate in the management of trans-boundary environmental problems. The programmatic activities of regimes which focus on improving the knowledge about the causes and effects of a problem or about the policy options that are available for problem solving can be understood as social processes “in which scientists, policymakers, and other stakeholders are (or are not) gathering data, conducting analysis, explaining, debating, learning, and interacting which each other around the issue on which the assessment focuses” (Clark, Mitchell and Cash 2006, 14).