This paper analyzes the implementation of a new tool of institutional cooperation in France, the Communaute d'agglomeration (Community of Urban Areas, CUAs). It does so by drawing upon 10 case studies of newly formed CUAs. CUAs are becoming increasingly common in France's historically fragmented system of local government. The paper begins by describing the rules of the new system and their political consequences. It then goes on to evaluate the salience of two competing explanations of political activity in relation to CUAs: territorial political culture (i.e. context) and institutional learning. The paper then assesses the relative importance of three dimensions of institutional building. The first is the political leadership. The second concerns the incentives for cooperation, focusing on financial support and the prefect's capacity to impose a process of municipal integration. The third is the democratic dimension of CUAs. Many politicians and scholars have criticized these institutions because of what is thought to be their democratic deficit. This discussion is then related to the more general debate about participatory and/or representative democracy in France.