Cities’ have multiple roles in climate-resilient development. This chapter explores cities as techno-social systems with complex metabolisms, networks and impacts beyond their boundaries. The chapter outlines how cities operate as sources of catalytic change through their complex production, exchange, innovation and governance systems. Therefore, we need to recognise cities as both part of the problem and part of the solution to climate change. This chapter explores the emergence of global networks of climate-active cities and how these are enabling networked governance, peer-to-peer learning and accelerating climate-resilient development. Nonetheless, more systemic changes are needed given the scale, urgency and magnitude of the international climate challenges.