Against the claim that behavioural patterns within the European Parliament are becoming more and more homogenized as a consequence of parliamentary professionalization and socialisation, this article argues that MEPs’ representational practices are irreducibly heterogeneous. Based on a sociology of roles, it points out the coherence and stability of the different ways in which the European mandate is exercised. Drawing on quantitative and interview data from the 5^th legislature (1999-2004), five ideal types of parliamentary roles can be distinguished : the Leader, the Specialist, the Intermediary, the Outsider and the Dilettante. This variety of role types can be interpreted as resulting from the aporiai and contradictions in representation at the EU level.