Scholars typically model the politics of global public goods or common pool resources as difficult collective action problems. Theories of international organization aim to explain how institutions can promote cooperation by solving the free rider problem. Based on an analysis of a quintessential global collective action problem—international climate mitigation—this article challenges both this diagnosis of the problem and the concomitant institutional remedies. Important elements of climate mitigation exhibit three key features that depart from the canonical model: joint goods, preference heterogeneity, and increasing returns. The presence of these features creates the possibility for “catalytic cooperation.” Under such conditions, the chief barrier to cooperation is not the threat of free riding but the lack of incentive to act in the first place. States and other actors seek to solve this problem by creating “catalytic institutions” that work to shift actors’ preferences and strategies toward cooperative outcomes over time. While catalytic institutions can be seen in many areas of world politics, the 2015 Paris Agreement on climate change has put this logic of cooperation at its core, raising the possibility that similar catalytic institutions may facilitate cooperation in other areas of world politics characterized by analogous problem structures.