How does civil society shape the development of cleavages? While intermediary organisations featured heavily in historical accounts, neo-cleavage theory often ignores meso-level dynamics beyond party politics. This agenda-setting article introduces a framework to study how civil society structures group–party linkages on the supply side and deepens social closure on the demand side. Hypotheses are developed on how changing civil society in Western Europe affects these functions. Evidence from expert and population surveys, plus case illustrations, suggests civil society continues to influence cleavage politics in differentiated and volatile ways.