This Element maps the relationship between taxation and social policy from a comparative and historical perspective. It critically reviews studies in fiscal sociology, history, political science and political economy to highlight blind spots in the body of knowledge that future studies could explore. It shows that exploring the revenue side of social policy offers compelling answers to central questions tackled in welfare state scholarship and addresses questions such as: What explains the introduction and timing of social programs? How can we understand processes of welfare state expansion and retrenchment? What determines the redistributive capacity of welfare states? What accounts for variations in redistributive capacity between groups and across generations in different countries? While bringing in the financing side of social policy complements prevailing accounts in the welfare state literature, studying financing can also transform how we understand social policy. This title is also available as Open Access on Cambridge Core.