The purpose of this PhD thesis is to examine how, in the context of the institutionalization of the European Union, a new category of political actors – members of the European Parliament or Eurodeputies - is created. Elected in national contexts, Eurodeputies are at the same time actors in a multileveled European space, with specific logics and political resources. More than just a juridical evolution or the result of ideological personal choices, the professionalization of French European delegates is tied to a transformation of the political uses of the European mandate. The emergence of European political careers is dependent on the practical logics adopted by Eurodeputies. These logics are a function of their personal political trajectories and the specificities of European political games. If historical sociology has shown that political professionalization is due to a process by which actors living “for” politics begin to live “of” politics, the reverse is happening here: actors living “of” Europe start to live “for” Europe, constructing thus a new political and social entity. This way, European delegates contribute to the social construction of a differentiated (and always divided) universe of political practices and representations of the world, space and time.