While challenger parties are on the rise in Europe, there has been little attention paid so far to their organization. Even though new parties enjoying path-breaking electoral success soon after their foundation tend to lose votes at their second electoral contests, due among other things to their organizational structures, some parties stand as exceptions. Among them, the Five-star Movement is the most prominent such party in Europe. The party has undergone a number of major organizational changes in the last 10 years, which have halted its institutionalization process, but whose impact on electoral success were, at first sight, less relevant. How did the party deal with the issue of internal reforms and how did these internal reforms change the party structure? This article retraces the party's transformations and tests hypotheses related to three competing interpretations of the Movement's organization: those that see it as a business-firm party, a franchise party and a party movement. Eleven years after its foundation, I contend that the Movement should now be analysed as a 'plebiscitarian' movement party.