The debate about the definition of Public Service is led in France by lawyers. The aim of the present study is to illustrate the notion that economists as well as academics and engineers took a part in this controversy.Two examples are particularly noteworthy.The first is related to the interwar period and the well known opposite points of views of Francis Trevoux, who favored American Institutionalism, and Henry Laufenburger who was a supporter of State intervention based on the French administrative law. The second example is that of Maurice Allais, a neo-liberal engineer, who refused after 1945 both interventionism and the legacy of the French services publics économiques.