Trade union movements in Europe are confronting multiple challenges. Among the adversities that union leaders face are pressing organisational problems: membership erosion due to structural changes in the economy and society; unfavourable political and institutional conditions that make organizing even more difficult; and attempts to attract and represent new social groups remain insufficient. ‘Deunionisation’ and its consequences for collective bargaining and for the political clout of union movements has become a problem acknowledged not only in academic but also in union circles. However, these accounts rarely note the intricate relationship between union movements and welfare states, and the potential consequences of ongoing efforts to recalibrate the welfare state, which unions helped expand. Facing decline in membership, representativity, and dues income, we could expect unions to become more dependent on the welfare state in which they are embedded. Where they have institutionalized involvement in statutory workplace representation or play a role in the co-management of social and employment policies, they could gain additional legitimacy and resources. Where unions are weak in membership strength and bargaining power, they may still benefit from the bargaining coverage through better-organised employer organisations or from state support via legal extension of collective agreements to non-organised workers and non-unionised firms. In addition, the welfare state might provide several ‘union securities’, be it through union-friendly labour relations in the public sector or subsidies to collective insurance schemes run by unions. Moreover, as social movements, organised labour may be able to assume a role in the politics of welfare state reform, defending the interests of current and former wage earners against government and employer policies. In recent years, some union movements have been capable of blocking reform efforts, while in other cases, union leaders were willing to negotiate the adaptation of labour market and social policies to the current domestic and international challenges.