On the matter of presidentialization, France has been considered a “quasi-experimental case” (Samuels, 2002, p. 463) in so far as it shifted from a parliamentary system during the Fourth Republic to a presidentialized one during the Fifth Republic. Introduced in 1958, the process of presidentialization has developed step by step and differently affected political parties. To what extent did institutional change impact the French party system? What forms did presidentialization take? This chapter addresses both of these questions by focusing on two major French parties, the Socialist Party (the Parti Socialiste, PS) and the neo-Gaullist Party (the Union pour un Mouvement Populaire, UMP). Even though their domination over the presidential race has been challenged in 2002 by the extreme right Front National (FN) (its leader, Jean-Marie Le Pen, overtook Lionel Jospin in the presidential first round), they still prevail over the others (Grunberg and Haegel, 2008): since 1981 every President of the Republic, François Mitterrand, Jacques Chirac, Nicolas Sarkozy, and François Hollande, came from one of these parties.