The article proposes a reflection on the organizational adaptation of political parties, exploring the linkages between party regulation and party organizational change. By building on an institutional approach, we maintain, against conventional wisdom, that resilience of party organizational dimensions prevails and corresponds to persistence in the regulative structures of politics. Empirically, our study focuses on the established political parties of five Western European democracies from 1970s to 2010s, through an in-depth analysis of the parties' core organizational features (membership, party income, internal structures and decision-making procedures) and of the main sources of party law.