This chapter focuses on the importance of these institutional factors, particularly electoral rules, in shaping party opposition to the EU through a case study of French European elections over thirty years. The transformation of party financing and European electoral rules during the reform of 2003 successively opened and closed specific opportunities for anti-EU parties in French politics. Analysing these evolutions in the French case provides a means to uncover some empirical elements across different theoretical frameworks. Two main effects on French opposition to the EU have become apparent. The most important one is probably the fact that this new context had a different impact on small and medium-sized Eurosceptic organizations. It benefitted the latter while making it harder for small and single-issue or new parties to capitalize on European elections. The second effect is that parties adapted by building ad hoc coalitions for these elections.