Cities consume more than 60% of global energy and that share is rising with the rapid rate of urbanization. With cities playing a crucial role in sustainable energy and climate systems, this article examines emerging efforts by cities around the world to shift to a development pattern with less energy and less carbon. We review metrics that define a low carbon city and present key steps in low carbon development. We examine city-level inventory methods and target setting. Much of the article is devoted to examples of policy measures that cities are pursuing to save energy and carbon, from net-zero buildings and 20-min neighborhoods to distributed and renewable urban energy supply.