This thesis compares six citizen debt audit groups in France, Spain, and Belgium. Mobilised from the debt crisis in several European countries at the beginning of the 2010s, citizen-auditors criticise how public authorities intervened in the crisis management, likening it to a dispossession of the capacity of public authorities to act against the most lucrative interests of private financial and economic actors. Such activists therefore advocate for the implementation of mechanisms of surveillance and control of the governed over the powerholders, to control of both the form of financial decisions (opening up the debate on public finances which must be transparent and understandable for any citizen) and their substance (monitoring that public decisions contribute to the interests of the social majority of the population). Through the citizen audit, they assess the democratic quality of their political system, one of the criteria of which is the government's capacity to promote the social progress of its citizens. To that extent, they participate in the definitional struggles over what democracy should be. In this thesis, we have chosen to analyse citizen audit mobilisations through the prism of the figure of the 'citizen-monitor', to highlight political behaviours and forms political participation beyond the vote that have not yet been sufficiently studied. We have carried out an analysis by contrasts and similarities. We put forward how these activists commonly strive to impose themselves as intermediaries between decision-makers and citizens, participating de facto to the production of partisan action as well as public action, in the political spaces where they mobilise. ; Cette thèse porte sur la comparaison de six collectifs d’audit citoyen de la dette, en France, en Espagne et en Belgique. Mobilisés à partir de la crise de la dette en Europe, à l’aube des années 2010, les auditeurs-citoyens critiquent la manière dont les pouvoirs publics sont intervenus dans la gestion de la crise, assimilant cette dernière ...