This thesis takes as its starting point the study of a police service, the Police Aux Frontières (PAF) in connection with European integration. Drawing inspiration from the sociology of the State, we have developed analytical categories capable of reflecting the concomitant evolution of this police force and the national and European ‘traffic regimes’. The ‘traffic regime’ is defined by the Roman categories of the State’s analysis: it is linked to a ‘political centre’ and defines a relevant territory of movement and the characteristics of the persons entitled to travel there. The PAF is characterised as a travel police and involves some of the forms of state power described by Michel Foucault, which focuses on the state’s ability to remotely control the activities of individuals. The national movement regime has been based on the border principle since 1974 as a legitimate and effective place for checks on movements of persons and deviations. It is at odds with that of the European traffic regime, which, from 1985 onwards, is based on the principle of free movement across internal borders. The PAF, a marginal administration, then undergoes an unprecedented increase in its staffing, tasks and role in the design of the traffic regime. It manages the interactions and contradictions between the national and European traffic regime. The PAF appears to be both a professional actor able to defend an extension of the boundaries of its ‘jurisdiction’, but also an administrative actor involved in the development of traffic regimes.