The paper investigates how far Hong Kong and Singapore, by ‘acting global’ through transnational networks, are ‘thinking urban’ in terms of advancing their own particular climate policy agendas within their own distinctive political and geographical contexts. This inquiry entails a three-pronged analysis, addressing firstly the purpose, structure, activities and impacts of the two networks C40 and SEANCC; secondly, the engagement of Singapore and Hong Kong in their respective networks – in terms of their motives for joining, networking practices and effects of membership – and; thirdly, the nature of urban agency in transnational networks, drawn from a comparative interpretation of the findings. The paper draws conclusions on the similarities and differences between the two networks as well as between the two cities working in them. More generally, it points to the multiple ways in which the local and the global interact in urban networks and explains how this can raise our understanding of the ‘urban’ in climate mitigation.