This chapter discusses the truth to power which is a major theme in political science and policy studies, commentators are increasingly skeptical about whether modelers and scientists are capable of developing truth, and whether power ever listens to them anyhow. Sustainable development is one of the major mantras invoked in the area of international environmental governance. Sustainable development was popularized in the seminal 1987 World Commission on Environment and Development report, Our Common Future. The chapter explores the concept of usable knowledge. Usable knowledge encompasses a substantive core that makes it usable for policy-makers, and a procedural dimension that provides a mechanism for transmitting knowledge from the scientific community to the policy world and provides for agency when theorizing about broader patterns of social learning, policy-making, and international relations. The UN Economic Commission for Europe (UNECE) and the International Institute for Applied Systems Analysis (IIASA) helped to develop and circulate usable knowledge for the effective management of European acid rain.