In this policy brief, Distinguished Fellow John Whalley and Research Assistant Sean Walsh assess some of the critical issues and obstacles standing in the path of a successful conclusion to the December 2009 climate change negotiation in Copenhagen. Policy makers must address unresolved debates about the concept of “common yet differentiated responsibilities,” the measurement of emissions, the availability of international funds and the enforcement of international agreements. The negotiation is complicated by the relationships between environmental policy and other international systems, such as trade. There are, furthermore, significantly different estimates of the potential consequences of climate change. Despite the numerous obstacles, the authors are optimistic that the political will to reach an agreement in Copenhagen remains strong.