This book investigates why and how several contemporary populist radical right parties (PRRPs) in Western Europe adopt the supposedly outdated mass party organizational model. While the first half of the twentieth century saw the rise of political organizations which were rooted in local communities and characterized by clearly identifiable ideologies, the so-called mass parties, this organizational model is now widely assumed to belong to the past. Citizens are seen to disengage from party politics, and in an age of mass and new social media, old as well as new parties can reach out to the electorate without the need for extensive face-to-face interaction. However, the mass party model has proven to be resilient, and indeed successful among several PRRPs, which criticize established parties precisely for having lost touch with ordinary citizens. Through an analysis of party structures and interviews with 125 PRRP elites and 100 active members, the book opens the black box of four populist radical right mass party organizations in Belgium, Finland, Italy, and Switzerland. The study finds that party elites consider the mass party model advantageous to their party’s electoral goals, organizational functioning, and survival. In addition, the book shows how a collective sense of efficacy is key in keeping activist members motivated to invest time and effort in party activities, despite experiencing stigmatization and receiving few concrete benefits in return. Based on its findings, the book re-evaluates received wisdoms of party organization theory, and shows how traditional forms of party organization adapt to changing political contexts and communication environments.