International treaty law tends to assume that when treaties are negotiated between countries, they are negotiated by well-informed negotiators with a thorough understanding of the issues and interests at stake. In providing the basic data that are used by negotiators and policymakers to determine how problems should be addressed, science and scientific communities have an important role to play in influencing treaty negotiation. This chapter explores the regional problem of "acid deposition" and the global problems of the depletion of the ozone layer and climate change. Regional air pollution can cause damage to infrastructure, ecological systems, and human health, and is being dealt with by the agreements in the regime on Long Range Transboundary Air Pollution (LRTAP). The chapter discusses the use of knowledge, power, and participation in the three regimes such as LRTAP regime, ozone layer regime and climate regime. It considers how scientific consensus influences the negotiations, the regional imbalance in knowledge, and normative issues.