Construction of the Legitimacy of Funding Agencies: the Case of the Swiss National Found of Scientific Research (1940-2000) In some countries, public research is financed by funding agencies. Those agencies operate not only on scientific production, but also on researchers’ credibility cycles. They can be therefore considered as an established power of scientific authority in so far as they participate in distribution of material and ideal means within the scientific field. This paper is concerned about those agencies’ kind of legitimacy and is interested to explore how this legitimacy is constructed. The legitimacy question is interesting in so far as those agencies hold an intermediate position between the political field and the scientific one, that oblige them to consider several social requests. This relational configuration is potentially a tension source in term of legitimacy conception. And because legitimacy is connected with the state of battle of wills and meaning between the political field and the scientific one at a given time of the history of a country, this legitimacy can be put in question. Then, in order to report on plurality of legitimating practices and on its contingence, it’s advisable to develop this analysis on a long time. This paper offers an analysis of the constitution of the legitimacy of one of this agency the Swiss national found of scientific research. Three main periods have been detected the fifties with the creation of the Swiss national found of scientific research and the setting up of grants for fundamental research ; the seventies with the elaboration of national programs aimed to focus research on some defined targets and the nineties with the creation of national poles of research. The three periods shows that legitimating practices are constituent of power relationship and participate to the transformation of the equilibrium between the political field and the scientific one. In an ideal-type way, the evolution of practices of national fund and of its organization can be presented in the following way: in the first period (1950-1960), the national fund receives its legitimacy both from the scientific values and norms and from political institutions. In the second period (1970), the equilibrium is modified as the legitimating practices of the national fund change. These practices are based much more on a political use of science partially altering, as a result, the evaluation criterions of research. Finally, in the third period (1990), the national fund tries to rely its legitimacy much more on scientists in order to gain independence as to politics.