Economic science has penetrated the main places of power and feeds daily into public and private actions. It is involved in the construction of states and markets. Through the development of economic expertise in the steering bodies of the global economy, it has gained a central and major role in every sector of public policy. We describe the way economics has conquered this dominant position through a combination of internal and external structuration, and we discuss the current emergence of new epistemological and methodological conceptions, still dominated but possibly very central in the coming years and their possible consequence with regard to public policy. This is especially the case with behavioural economics.