The role of cities in shaping and driving the decarbonization process is growing, as municipalities are increasingly implementing policies and technologies that support the transition to a low-carbon economy. Cities are leading the shift to sustainable energy consumption and production, reducing emissions from urban and national transportation fleets, and adopting “smart” technologies and other innovative measures to efficiently use and manage resources. Forerunner cities deserve special attention in this regard, as they may shed light on the capabilities and limitations of cities in a given political system.