Abstract: In 2009, the Obama Administration entered office in the midst of a serious economic recession. Nonetheless, one of its priorities was to address the problem of climate change. It ultimately did a great deal -- producing, with the aid of market forces, significant reductions in greenhouse gas emissions, which ultimately helped make an international agreement possible. This essay offers a preliminary account of some of the central domestic reforms, including the “endangerment finding”; the selection of a social cost of carbon; fuel economy regulations for motor vehicles; controls on new and existing power plants; and energy efficiency regulations. At various points, potentially challenging issues of law and policy are identified, and different imaginable paths are specified. The essay can be taken as an account of the extent to which the executive branch, relying on pre-existing regulatory authorities, can accomplish a great deal in an area in which the national legislature is blocked. To that extent, the climate change initiatives offer an illuminating case study in the contemporary operation of the system of separation of powers. There is a brief discussion of whether the reforms are likely to prove enduring. Appendices offer an assortment of tables on relevant costs and benefits.