The C40 is in many ways a success story. It has generated increased engagement and coordination, with the vast majority of member cities now committed to the collective goal of carbon neutrality by midcentury. This level of coordination was virtually unthinkable a mere decade ago, and the theory of global urban governance fields helps to identify and explain its origins and underpinnings. The ability of the C40 to generate convergence and consolidation around a common understanding of how to “be” a global urban climate governor has enabled the C40 to generate collective effort in the face of voluntary participation. This chapter sets out the ways in which this insight contributes to pushing forward the scholarship on cities, global climate governance, and the role of cities in international relations more broadly. It also highlights important questions that emerge as a result, including the relationship between the content of C40 norm/identity convergence and the potential contribution it can make to achieving collective goals of decarbonization and transformative sustainability, how to measure and assess progress and performance, and for whom/to whom cities are rendering themselves accountable as global climate governors.