We propose a theory of the welfare state, in which social transfers are chosen by a governing group interacting with non-governing groups repeatedly. Social demands from the non-governing groups are credible because these groups have the ability to generate social conflict. In this context social insurance is supplied as an equilibrium response to income risks within a self-enforcing social contract. When we explore the implications of such a view of the social contract, we find four main determinants of the welfare state: the degree of aggregate income risk; the heterogeneity of group-specific income risks; the public administration’s ability to implement group-specific transfers; and the ability of the non-governing groups to coordinate their social demands. We also analyze the link between public good provision and social insurance.