Despite these predictions and their potentially widespread consequences, relatively little is actually known about the nature of party membership in a comparative sense (Heidar 2006), and the role and relevance of party members today. Forming a more critical understanding of what party membership is – including what it formally means to join a political party, what motivates citizens to join, and what activities they undertake once they have joined – is crucial to assessing the true extent of the trend of declining engagement with political parties. From a reform perspective, knowing why members join and how they participate is the first step in re-imagining political parties that are more responsive to the preferences of citizens today. At a time when relatively few participate in party politics and of widespread public disaffection with formal political institutions (Hooghe and Zmerli 2011), knowing the characteristics of who joins, and what opinions they hold, gives us some insight into a class of citizens who may now potentially form part of the political elite (Hooghe and Kern 2013; van Biezen 2014).