The Social Policy Indicators (SPIN) database provides the foundations for new comparative and longitudinal research on causes and consequences of welfare states. Building on T.H. Marshall’s ideas about social citizenship, SPIN makes available comparative data on social rights and duties of citizens, thereby moving research beyond analyses of welfare state expenditures. The SPIN database is instead oriented towards analyses of institutions as manifested in social policy legislation. Data are carefully collected in a coherent and consistent methodological manner to facilitate quantitative research of social policy across time and space. To date, SPIN covers 36 countries, of which several have data on core social policy programs from 1930 to 2019.