Since the economic crisis of the 1970s, welfare state reform is on the political agenda of advanced welfare states facing multiple economic and sociodemographic challenges. The public debate and initial research (in particular, the new politics thesis) focused on the question why welfare retrenchment, the cutting back of public expenditure, has met much public resistance. More recent research studies the variations in welfare restructuring as complex adjustments to multiple challenges, while seeking to explain these changes through compound factors: ideational, institutional, and interest-based explanations.