Introduction Empirical research on party membership in Germany dates back to the early 1970s. This is probably no coincidence, as it was the time when hundreds of thousands of new members entered the three catch-all parties, the Christian Democratic Union (CDU), its regionalist sister party Christian Social Union (CSU), and the Social Democratic Party (SPD). The focus of scholarly work during this period was on the motives of the new members joining the parties, and the changes this development brought for the social structure of party membership (Diederich 1973; Güllner 1977; Meyenberg 1978; Falke 1982). But this focus of research changed dramatically in the 1990s: membership of the three major parties was already stagnating in the 1980s, and even the signifi cant expansion of the electorate in the course of German reunifi cation in 1990 could not prevent a massive drop-off in party membership in the 1990s. The debate about party membership changed considerably, from stressing the vigour and strength of the party base to a story of decline and decay, with some authors announcing the ‘end of the membershipbased party’ (see Wiesendahl 2006: 11-15). A less alarmist view sees this decline more as a process of normalization after a phase of extremely high politicization (Scarrow 2000: 86; Wiesendahl 2006: 103; Klein et al. 2011: 19-20). In any case, the main questions in German scholarly research changed to an explanation of the decline in membership, considering changed incentives to join the political parties as well as motives for leaving them (Heinrich et al. 2002; Spier et al. 2011).