Abstract : During the 20th century, the decentralization and the regionalization reforms have deeply modified the running of the local institutions and the relationship they each other have. Through the study of the public policies of transports implemented in Brittany since the middle of the 19th century, we have underlined the impact of those reforms on policy leading. The developments of organizational learning and of new management system by the authorities responsible of transport have carried these changes out. Through the leading of their public transports policy, local authorities have developed their skills of transportation organizer. Consequently, the competition has grown between the different local authorities in charge of transports, mainly between the region and the departments. Thus, the traditional arrangements between the Breton local authorities were disrupted by decentralization and regionalization. In order to balance the public policies and to manage their consistency on its area, Brittany region has settled a monitoring system which gather all the local councillors in charge of the transports in Brittany. Through the development of concerted projects, a regional monitoring system is gradually built. This system that we call "régional meso-governance" and which we modelize in this thesis, constitutes an hybrid model in middle way between a local government organisation and a territorial governance.