Social investment is a strategy that addresses neoliberal austerity by putting private capital to public purpose. An investment state serves as a sequel to the welfare state by maximizing capability, expanding employee benefits, implementing evidence-based policy, democratizing polity and commerce, and advancing social and institutional inclusion. The Investment State provides a template for future social policy, which can be adapted to cities, states, nations, and international trade agreements. It serves as a sequel to the author's previous book, The Dynamic Welfare State (OUP, 2016) -- which included a theory of welfare state decline -- by envisioning a new paradigm for social programs.