We review the main theoretical conclusions from a quarter century of comparative studies of welfare states in the affluent democracies. We contrast early debates over the relative importance of industrialization, economic growth, and social classes for explaining welfare state differences with contemporary claims about the role of globalization, postindustrialism, and gender relations in shaping their futures. We evaluate the claims against recent empirical evidence with the aim of highlighting both important lessons from the past and promising directions for future analysis.