The adoption of (open) primary elections can be considered one of the most relevant democratic innovations implemented by Italian parties in the last two decades. The PD has managed to introduce and then institutionalize this new participatory mechanism in a party system previously characterized by low levels of intra-party democracy. In this edited book we explore the functioning of primary election processes and assess their consequences at meso-level, on party organizational features, and at systemic level, on public debate, media coverage and electoral dynamics. What emerges from our analyses is primaries strengthen the participatory dimension of an electorally oriented party such as the PD, which is abandoning its (post) mass-membership party organizational features and is going towards more catch-all organizational features. However, primaries guarantee the stability of the relationship between grassroots members and the party as well as the viability of the PD’s organizational settings in the long run. Primary elections, as any political process, could bring unexpected results and even malfunctions, but their positive effects on the party and on the electoral dynamics, for the moment, exceed their shortcomings in the eye of both party elites and party members and voters.