Abstract:Since 2013, the Chinese central government has pushed cooperation on environmental governance in Urban Agglomerations (UAs). In some of these UAs, cities have previously been developing environmental governance activities autonomously, in the absence of inter-city cooperation, while on others, spontaneous cooperation has previously taken place. These differences in historical context provide us with an opportunity to study, in a comparative way, how a history of cooperation influences the effectiveness of inter-city cooperation on environmental governance. Our approach to carrying out this comparison is to reconstruct the trajectories of events that describe the evolution of environmental governance in two UAs (Beijing-Tianjin-Hebei and Yangtze River Delta), covering the period from the early 90s to 2016. The main findings of this study are that the trajectory of environmental governance in a historical context of prior spontaneous cooperation is more effective in achieving goal intertwinement than that in a historical context of no prior cooperation; and that informal forms of cooperation, along with decentralized coordination by local actors, are critical and more influential in bringing about more effective cooperation. On the other hand, in a historical context of no prior cooperation there is an opportunity to design a cooperative structure from scratch; in this process attention should be paid to the creation of an equal playing ground, with balanced costs and benefits for all partners. By contrast, cooperation on environmental governance in a context where there is a history of spontaneous cooperation the central government can still play a role in the further facilitation of cooperation.