The difficult government of health by the market.

Summary By taking as its object a public policy measure to combat obesity, this article emphasizes the conditions for building trust in a public action mechanism. These conditions are all the more demanding when, as in the case of the voluntary nutritional progress charters studied, a public action instrument is intended to initiate market dynamics. Far from being guaranteed by the support of public authorities alone, the effectiveness of such a tool also depends, in a decisive way, on its capacity to ensure the alignment of the interests of the parties it brings together (public authorities, but also industrial economic actors). This alignment of interests is nevertheless undermined by the management of the mechanism which, guided by the concern to preserve its reputation, undermines its effectiveness by regularly contributing to the misalignment of the parties' interests.