The literature on the determinants of welfare state effort displays many inconsistencies and contradictins. This article takes imoprtant stepts toward resolving these issues with the use of pooled cross-sectional and time-series analyses. The findings are that various independent variables affect different measures of welfare state effort in different and theoretically meaningful ways. Of special importance are the contrasting effects of Christian democracy and social democracy on transfer payments, social benefits expenditure, and total government revenue. There is also a strong effect of constitutional structure on welfare state effort, a finding that provides the first solid support for the state-centered perspective in a quantitative analysis.