The institutionalisation of a public offer of participation has brought about the emergence of a new category of public servants, specifically in charge of administrating the participation (design, organisation, animation of the participatory procedures). However, the administrative domestication of public participation remains still understudied. Based on empirical studies focused on french administrations, we argue that analysing the work of these agents is fruitful to understand, beyond the democratic rhetoric, what public participation means. Whereas, these professionals consider public participation as a way to modernise the bureaucracy in order to make fairest policies, more reactive to citizens’ demands, empirical study of the administrative and technical aspects of participatory policy highlights how this “politics” turn into bureaucracy. As public agents in charge of participatory policy fail to cause depth transformations of the administrative process with public participation, participatory policies became an autonomous policy sector. In order to try to demonstrate the usefulness of participatory policy, and legitimate their very existence, these agents spend a growing time in producing participatory innovations and more over in producing “traces” of effective change and effects of their activities : participants and their propositions are measured, their “work” are reported and filmed, the quality of the process is evaluated, and even so certified, and rewarded. As a matter of fact, the public authorities produce participatory devices without any true concern about their usefulness and the social demands that they should satisfy.