Beyond the sociological definition of a profession which offers rather static perspectives, the notion of professionalisation as a process provides several ways to understand the nature and change of cultural policies. In the field of central-local relationships, it is thus necessary to analyse the combination of a plurality of capacities, interests, and values to explain the specific influence of professionalism on policymaking. All these elements have been found from a case study of the creation and implementation of a music festival in a city in southern France (Montpellier). Professionalisation can indeed be considered as a key notion with which to understand both urban cultural policies as a whole and the implementation of a single cultural project.