Institutional transformations in recent decades have limited the weight and power of collective actors. Notwithstanding this, literature on employer associations (EAs) has argued a resilient performance in terms of affiliation. In this paper, we use comparative institutional analysis to evaluate the actual scope of these associations in terms of membership and the share of workforce employed by their members. Moreover, by utilising a logistic regression approach we delve into the drivers of the choice to join these organisations. Our results show a general decline of EAs, and point to large manufacturing companies as the great reservoirs of affiliation. However, institutional variations across Europe cause significant differences between countries. We thus demonstrate how membership is strongly influenced by the institutional framework, the relevance of the variables related to the provision of collective goods as a counterbalance to trade union activity and adherence to collective bargaining schemes.