The institutional turn in metropolitan governance has been influenced to a considerable degree by a rational choice approach, which views metropolitan governance as essentially created by local actors to reduce the transaction costs of inter-jurisdictional public-service provision. Another influential theoretical route follows a historical approach, which emphasizes the role of the state structure in producing formal institutions to enable governance at the regional level. Both approaches tend to be formalistic, simplistic and deterministic in nature, thus neglecting the dynamic interactions between the actors and their more informal, intangible, yet more basic, legitimate institutions, such as culture. This article examines the dynamic role of culture in metropolitan governance building in the context of decentralizing Indonesia. The analysis focuses on ‘best-practice’ experiences of metropolitan cooperation in greater Yogyakarta, where three neighbouring local governments known as Kartamantul have collaboratively performed cross-border infrastructure development to deal with the consequences of extended urbanization. We draw on sociological institutionalism to argue that building this metropolitan cooperation has its roots in the capacity of the actors to use and mobilize culture as a resource for collaborative action.