In this article, we discuss the role of trade unions in the evolution of occupational pensions in four countries: Austria, Belgium, Germany, and the Netherlands. In all four cases, important reforms have been made to the pension systems, including the consolidation of extensive occupational pensions in the Netherlands, substantial expansion of occupational pensions in Germany, and a continued marginal position of occupational pensions in Austria and Belgium. We show that the distinct developments in occupational pensions in the four cases since the 1990s can, to an important extent, be understood by the differences in the power resources and preferences of trade unions. The influence of unions on the development of occupational pension systems depends, on the one hand, on the extent to which they see them as an opportunity or a threat, and, on the other hand, on the extent to which they have the power resources to consolidate, oppose or shape these systems.