Advanced welfare states seem remarkably stable at fi rst glance. Although most member states of the European Union (EU) have undertaken comprehensive welfare reform, especially since the 1990s, much comparative welfare state analysis portrays a 'frozen welfare landscape' . Social spending is stable. However, if we interpret the welfare state as more than aggregate social spending and look at long-term trends, we can see profound transformations across several policy areas, ranging from labour market policy and regulation, industrial relations, social protection, social services like child care and education, pensions, and long-term care. Th is series is about trajectories of change. Have there been path-breaking welfare innovations or simply attempts at political reconsolidation? What new policies have been added, and with what consequences for competitiveness, employment, income equality and poverty, gender relations, human capital formation, and fi scal sustainability? What is the role of the European Union in shaping national welfare state reform? Are advanced welfare states moving in a similar or even convergent direction, or are they embarking on ever more divergent trajectories of change? Th ese issues raise fundamental questions about the politics of reform. If policymakers do engage in major reforms (despite the numerous institutional, political and policy obstacles), what factors enable them to do so? While the overriding objective of the series is to trace trajectories of contemporary welfare state reform, the editors also invite the submission of manuscripts which focus on theorizing institutional change in the social policy arena.