Minimum income protection (MIP) determines the disposable income a person obtains when she has no market or social insurance income, few assets and no family support. This last-recourse income, usually social assistance benefits plus associated transfers, constitutes a significant indicator of a country’s commitment to social justice. Yet, we know little about the politics of MIP, in part because welfare state scholars have focused on more encompassing social insurance programmes, and in part because of a lack of good comparative data. This article takes the measure of MIP adequacy in 18 OECD countries for the 1990–2010 period, for single, able-to-work individuals, tracks its comparative evolution, and proposes an explanation of its determinants, with a times-series cross-sectional model. The main positive determinant of adequacy is a generous welfare state; the main negative force is the importance of the public debt. Overall, the politics of MIP appears consistent with that of the welfare state.