“How to become a party’s official candidate in France? Members of Parliament’s interpretations of the selection rules and practices in the PS and the UMP for the 2007 and 2012 legislative elections” – French political parties have to face the challenge of internal democratization of candidate selection. The selection is one of the most important party-related moments for aspirants during their political career: being selected means becoming a party’s official candidate. This article focuses on the interpretations of the selection rules and practices within a party. The aim is to look beyond the public image given by political parties, especially regarding internal democratization. Three research questions are addressed in this work: What is the impact of the selection mode on the conduct of aspirants? What interpretations are given by MPs, as winners of the selection and the election? Is it possible to identify some strategic or adaptive behaviour from the aspirants, considering the selection rules of the parties? The relevance of the theoretical hypothesis about the nature of the selectorate (inclusive/exclusive) is tested, based on France’s two major parties, the Parti socialiste (PS) and the Union pour un mouvement populaire (UMP). The analysis uses both “normative rules” (party statutes and rules) and “pragmatic rules” (declared behaviour from former aspirants, collected through interviews with MPs). Beyond some written differences about the selectorate in the formal rules, the behaviour of aspirants is almost the same in both parties: pragmatic rules have more influence than official rules; therefore, the official selection rules are not the primary concern for aspirants who wish to be selected. What matters and what differentiates aspirants’ behaviour is the degree of political seniority: the incumbent effect remains very strong, despite the democratization of the procedures.