The French system of local and regional government has long been characterised by several features (Mabileau, 1994). The first is the institutional fragmentation without comparison anywhere else in Europe : 36 700 municipalities, as much as in the 14 other EU member states put together. The second is the multiple office holding (cumul des mandats) that enabled local politicians, until some limitations were enforced, to be mayors, members of département and regional assemblies and MP, and sometimes ministers. This practice was not only a way to extend and secure political control, but also to gain access to the central government's resources in order to implement policies at the constituency level . This system gave birth to a specific political breed, the notables, those politicians who where outrageously dominating local political spaces because of their personal prestige and their privileged access to central government and administrations. Those notables were often competing against each other to gain resources from the central government and to influence national policies (Grémion, 1976). In some way, and this is the third peculiarity of the French local and regional government system, this permanent competition between local and regional politicians has long been seen as an asset for the State's field services, and for the Prefect in the first place. The central government representatives at the field level were able to use this competition to impose some of their choices and priorities. For a long time, all these features have not made cooperation a salient aspect of local and regional governance. Competition was rather the rule and the 1982 Decentralization reforms did nothing to change this situation. Nevertheless, things recently changed in France and cooperation managed to nestle in the French local government system. In this paper, we will distinguish two different kinds of cooperation : on one hand, we will deal with horizontal cooperation, i.e. forms of cooperation linking authorities of the same territorial level (in this perspective, we will mainly deal with inter-municipal cooperation) ; on the other hand, we will deal with vertical cooperation, i.e. forms of cooperation linking authorities of different territorial levels. The main arguments of this paper are the following. Firstly, the concern for horizontal cooperation came first, it is only very recently that the problem of vertical cooperation arose. The consolidation of horizontal cooperation practices mainly occurred between municipalities and has been crowned with the recent and spectacular reinforcement and/or multiplication of inter-municipal cooperation institutions. Nevertheless, and this is the second main point of the chapter, this cooperation, when it occurred, was not always the result of the creation of strong cooperation institutions but rather the outcome of the collective recognition of common stakes and problems and of the collective work on these common stakes and problems. Cooperation has often been gradual, incremental and problem-driven. The third argument of the chapter is that it is the reinforcement of horizontal cooperation between municipalities that generated the urge for vertical cooperation, mainly between reinforced inter-municipal cooperation institutions on one hand, and départements and regions on the other hand. The reinforcement of vertical cooperation occurred along quite the same process, i.e. problems came first, were collectively tackled, but mainly through informal arrangements.