AbstractThis review essay takes stock of the recent literature about the role of ideas in social policy, with a particular focus on a key issue in social policy research: the changing interactions between states and markets over time. Specifically, our aim is to examine how the ideational literature discusses and explains prominent contemporary social policy evolutions: the rise of social investment and the financialization and technocratization of the welfare state. This is done based on the scholarship on state/market interactions and the role of ideas in social policy, and by utilizing key insights of scholars of ideational influences on state/market interactions. The article ends with a short agenda for future research on ideas and discourses as a crucial factor in the evolution of the welfare state as a key space in which states and markets interact.