Président du jury: Claude Grasland (Univ. Paris7) Directeur de thèse: Jacques Malézieux (Univ. Paris 1) Rapporteur: Jean-Pierre Renard (Univ. d'Artois) Rapporteur: Christian Vandermotten (Univ. Libre de Bruxelles) Expert: Philippe Doucet (secrétariat Interreg Europe du Nord-Ouest) ; What is the evolution of EU internal boundaries in the context of an increasing European integration? This research focuses on the spatial nature of the boundaries, at the moment they change, in terms of discontinuity and barrier effect. The research field is the boundary between France and Belgium, from the coast to Lille. The evolution of spontaneous border relations between populations is mainly carried through an analysis of mixed marriages for the last decades, at a local scale and at a national scale. As one of the main outputs, the contacts are growing between the Belgians and the French in the whole national territories, but there is no major change in the border zone. In other terms, the border effects spread at the national scale. And paradoxically, there are less close relations between the Flemish from France and Belgium. The reason for that stands in the increasing linguistic divergence between both sides of the border. The border change is also institutional, with customs redeployment and cross border / transnational cooperation emergence. These transformations imply a change in terms of spatial scale: the transnational / European scale looks more and more relevant to understand and manage border matters. ; Comment évoluent les frontières intérieures de l'Union européenne dans le contexte d'une intégration européenne toujours croissante ? Cette recherche porte sur la nature spatiale des frontières, au moment où celle-ci se transforme tant en termes de discontinuité que d'effet de barrière. Le terrain d'étude est la frontière franco-belge, du littoral jusqu'à Lille. L'évolution des relations frontalières spontanées entre populations repose en grande partie sur l'analyse de la nuptialité mixte depuis les dernières ...