This chapter describes and analyses the progressive spread of economic "expertise" in the sphere of public policy. It sketches the historical process of the expansion of economic expertise in France, and discusses the way it involves a reshaping of the relations between the State, markets, universities, and other relevant institutional entities (e.g., political parties, unions, etc.), as well as society in general. Considered from this socio-historical viewpoint, economic expertise seems to have contributed to the opening of State-centered regulation to more pluralistic and market-driven public policies in a number of sectors. The analysis draws more specifically on the case of health care, which has been engaged in a clear transformation from a traditional (welfare) State-centered regulation to more open and economically-driven policy. Various components of economic expertise and its concrete uses are under scrutiny, such as classic macroeconomic/econometric forecasting and conjunctural analysis; sectorial expertise; think tanks and organization-related expertise or counter-expertise; academic knowledge in the sphere of policy advice and decision-making; and the production and diffusion of economic discourse through newspapers, magazines, books, etc.