Résumé : This dissertation investigates how the support of national local and regional governments shape the European Citizens’ Initiative. By leveraging the author’s participant observation at Eumans, an organization promoting participatory democracy in the European Union, this dissertation assesses the contribution of local and regional governments, influencers, civil society organizations and politicians to the StopGlobalWarming.eu ECI campaign promoted by Eumans. To do so, the dimensions taken into consideration in the hypothesis relate to these actors’ contribution to the collection of signatures, media coverage and access to European institutions.The research relies on a theoretical framework built upon the concepts of “multipositional actors”, “reverse boomerang strategy” and two typologies of ECI organizers. The methodology used to collect data is mixed as it combines the author’s participant observation at Eumans with qualitative data stemming from interviews with the ECI organisers and quantitative data such as the numbers of signatures collected. Data has been analysed though the prisms of the concepts and typologies composing the theoretical framework. Ultimately, this dissertation makes the case for the involvement of local and regional authorities, such as mayors, district and regional councilors, in transnational ECI campaigns.As demonstrated by the StopGlobalWarming.eu ECI campaign, the support of this national local actors can be key to collecting signatures, getting media coverage to be featured in national public debates and, ultimately, to opening channels to get access to European institutions.