Territorial mobilizations concerning big infrastructural projects often become arenas of contention where expertise crosses political and technical claims. In the Italian case, the mobilization of expertise has been recently recognized by activists and intellectuals as one of the major traits of a rising «new environmentalism». The new aspect of this wave of collective action resides in the elaboration of alternative politics linking bottom-up communitarian knowledge with expert advice. This innovation addresses important questions for participation and democracy in general, since expert knowledge maintains indeed a delicate relation with democratic politics. In this paper I aim at analyzing how common citizens, political activists and experts participate in mobilizing expertise, constructing knowledge and finally contributing in making «technical democracy» work. I focus on a comparative study of mobilizations occurred in the city of Venice and Florence, given their importance for the rise of the so called «new environmentalism». Analyzing 4 protest campaigns I will shed lights on the mechanisms of co-production focusing on bottom-up expertise mobilization as well as on experts enrollment and their peculiar forms of engagement. In both cities I have selected 2 cases depending from their variation in conflict intensity and citizens’ participation. While in each city some problems tend to be confined in restricted mobilizations – regarding mainly activists and experts – others show high levels of participation and broader knowledge diffusion. Using a contentious politics approach, I investigate the social and political conditions characterizing these 4 protest campaigns together with the type of infrastructural projects. Crossing these two main dimensions – political conditions and technological factors – allows to look at the role of different expert cultures (professional and disciplinary habitus) and their interaction/intersection with political cultures (e.g. political ecologist, conservationist, environmentalist). This gives indeed the possibility to analyze practices and cultures at the border of politics and expertise. To get a general picture of the actors mobilizing I started conducting a media analysis on the main newspaper at the city level. I’ve integrated these informations with the analysis of documents produced by the different actors involved – from citizens groups to social movements organizations – like on-line web sources, newsletters, press release and dossiers, petitions, scientific articles and books. The main data have been gathered through an intensive ethnographic fieldwork in the cities, attending public meetings, assemblies, demonstrations and finally interviewing the main concerned actors. I conducted more than 50 in-depth interviews with public authorities, experts, activists and citizens playing a central role in the mobilization.