In the previous chapter, we demonstrated the emergence of public contestation and a degree of polarization over European issues between the social democratic and conservative party families in all three countries by the Ratification phase. In this chapter, we zoom in on the French ratification debate, because the French referendum stimulated the most intense contestation within our sample across the time-phases and countries. Again the primary focus is domestic party contestation. The story of the French referendum vote on the European Constitutional Treaty in 2005 has been told elsewhere (see Brouard and Tiberj 2006; Hainsworth 2006). Our aim here is to undertake a systematic empirical analysis of arguments and counter-arguments that parties used in their efforts to convince the public through the mass media to support, or reject, the Constitution. If politicization is underway within domestic national politics over integration, as many suggest (see Börzel and Risse 2009; de Wilde 2011; de Wilde and Zürn 2012; Hooghe and Marks 2009; Kriesi et al. 2008), then it makes sense to study one of its most prominent cases.