In the face of the federal government’s failure to tackle climate change in the early decades of this century, large cities in the U.S. started to take action. Networks of city governments and philanthropists offered cities support, and cities invested their own resources in sustainability offices. However, cities made limited progress in reducing their greenhouse gas emissions in the first two decades of this century. This book provides a clear-eyed analysis of the potential for big city governments to address society’s most pressing environmental problems, including limiting and adapting to climate change. It includes original case studies of New York’s environmental policy efforts in the first two decades of this century, which ground its analysis of the promise and perils of turning to cities to address climate change and other environmental issues. Drawing on the book’s analysis of cities’ strengths and weaknesses, it outlines a high-level agenda for urban environmental policy for the near term. With President Trump’s return to power in 2025, and his promises to undo many aspects of federal environmental law, it is more important than ever for environmental advocates and scholars to understand the potential and limits of local action to fill the gap.