jats:titleAbstract</jats:title>jats:pThe number of grassroots members of populist radical right (PRR) parties is on the rise, in contrast to the trend of membership decline in mainstream parties. While scholars have explained this by studying PRR parties' organizational strategies, I focus on party members and ask: Why do people join PRR parties? To answer this, I look not only at motivations, which is the dominant framework in party membership studies, but also at triggers – factors activating those motivations. Drawing on collective action scholarship, I argue that grievances and efficacy can work as triggers for joining PRR parties. Using interviews with 82 members of the Bharatiya Janata Party, the League in Italy and the Sweden Democrats, I uncover three elements in the path to PRR party membership: disaffection, affiliation and action. As well as questioning established narratives on why citizens join parties, my findings provide a novel theoretical framework to investigate this form of political participation.</jats:p>