This study examines the pillarised and partitocratic nature of Belgian political parties via an empirical overview of their party on the ground. Two main research questions guide the study: To what extent can party membership figures in Belgium be considered as ideal-typical of pillarised or partitocratic parties? And how does the social and political profile of party members in Belgium correspond to what one might expect from pillarised or partitocratic parties? The study relies on two types of data set: party membership figures since WWII and membership survey data of the four ‘dominant’ relatives in each party family in Belgium. The article shows contradicting results. Although party membership figures have nuanced the idea of partitocratic and pillar parties, the analysis of the profile of party members has produced more conclusive results. The members of some parties (PS, CD&V) still display a strong encapsulation in their sociological world, report specific reasons for joining, as well as lower levels of activism than in other parties.The pillar parties in Belgium seem to have reached a paradoxical situation in which their anchorage in civil society is still very strong, yet it relies on a shrinking social basis. These results raise the question of the incentives that parties offer to their party on the ground to mobilise citizens for participation. They indicate a need to look more systematically and empirically at this neglected aspect of party organisation, as it provides important information for the debate on party decline ; info:eu-repo/semantics/published