Ageing is one of the long-term challenges for old age security in Europe, in particular for the intergenerational contract of pay-as-you go public pensions. The comparative macro-sociological analysis maps the demographic trends, political constraints, and social policy reform dynamics across Europe. Due to demographic ageing all European societies face long-term sustainability problems of their pension systems. Despite many reforms, European welfare states differ in the timing of retirement and the extent of pay-as-you-go public pensions. The comparison of ten European welfare states reveals the cross-national variations in reducing early retirement and in partially shifting to prefunded pensions. In addition to financial sustainability, the contribution also discusses other sustainability issues, particularly social inequality and political feasibility, which must be overcome in addition to the demographic challenge.