This chapter describes the basic features and lasting influence on climate governance of the international system of states. When the problem of climate change became apparent, countries responded to it through diplomacy leading to international agreements for collective action. This chapter describes major aspects of this process. It summarizes how countries have negotiated a regime of international agreements and institutions intended to address climate change collectively and individually. A quarter-century was devoted to top-down measures – internationally agreed conventions and protocols setting out allowable greenhouse gas emissions for individual countries. More recently, the focus has been on bottom-up measures – nationally determined contributions to wider global efforts to govern climate change. While these efforts have resulted in a wide array of actions around the world to address climate change, they also demonstrate concretely the ways in which the international system, and the countries operating within it, have precluded aggressive collective action.