Belgium was the first industrialized country in continental Europe, but a modern nation-wide union movement developed rather late. Moreover, a number of pre-modern traits and social cleavages of ideological, linguistic and territorial origins cut across the class cleavage which emerged with industrialization. The strong interrelations between union movements and allied political parties crystallized into a pillared system of interest organizations divided by Weltanschauung. This has contributed to, and was reinforced by, a corporatist system of industrial relations, based on flexible co-operation between elites and supported by a clientelist Christian-Social welfare state. Unique among organized labour in Western Europe, the Christian union confederation is the largest in the country. Belgian unions are the only union movement in continental Europe (outside Scandinavia) that organizes more than half of the work-force. In addition to close ties with the political system and participation in national concertation, Belgian unions are involved in the administration and adjudication of unemployment insurance and have a strong presence at the workplace through union delegations and works councils. So far, most Belgian unions and their confederations have resisted pressures towards regional break-up which has marked Belgian politics during the past thirty years. Currently, A second consideration concerns the retention of membership after retirement. Adjustment of membership statistics is needed before comparable ‘net’ union density rates can be calculated.