On election day, voters’ commitment is crucial for political parties, but between elections members are an important resource for party organisations. However, membership figures have been dropping across parties and countries in the last decades. How does this trend affect parties’ organisation? Following classics in party politics research as well as contemporary organisational theory literature, this study tests some of the most longstanding hypotheses in political science regarding the effects of membership size change. According to organisational learning theory, membership decline should induce an expansion of the party organisation. However, threat-rigidity theory and the work of Robert Michels suggest that parties are downsizing their organisation to match the decline in membership size. To test the hypotheses, 47 parties in six European countries (Denmark, Germany, the Netherlands, Norway, Sweden and the United Kingdom) are followed annually between 1960 and 2010 on key organisational characteristics such as finances, professionalism and complexity. A total of 1,922 party-year observations are analysed. The results of multilevel modelling show that party membership decline triggers mixed effects. Declining membership size induces the employment of more staff, higher spending and a higher reliance on state subsidies. At the same time, it also triggers lower staff salaries and a reduction in the party's local presence. The findings indicate that today's parties are targeting an organisational structure that is custom-made for the electoral moment every four years. Faced with lasting membership decline, the party organisation retracts its organisational resources and focuses more on election day. Members matter to parties, but votes matter more.