We study the institutionalization of the European Parliament using a quantitative analysis based on biographies of elected members of the European Parliament over the period 2004 to 2009. The data underline the emergence of political work specialists able to ensure the leadership and control of the parliamentary space. The relative unattractiveness of the European Parliament compared to the national political space favors the recruitment of actors less endowed with legitimate resources. For a growing number of actors, the European Parliament represents an opportunity for professionalization and acquiring political capital. These sociopolitical transformations, along with institutional and juridical evolutions, favor the constitution of a “core” of specialists, able to acquire the space’s specific resources and to direct it.