“Land scarcity” is often accused of preventing housing production, in both public and private discourse; the disposal of unused or underused public land is then put forward as a solution to the "housing crisis". This phenomenon of privatization of public land has already been well documented, particularly in the United Kingdom, but also on state land (railway and military) in France and Italy. On the other hand, there is less information on the privatization of land in municipalities and their groupings in France, and even less on the effects of this privatization on construction, particularly housing. Yet the surge in land and property prices since the 2000s incentivizes private actors to maximize profits in markets, which produces land speculation and hoarding; the capacity for public intervention is reduced because there are fewer acquisition opportunities, more competition and higher costs. In this context, do local authorities have the capacity to play their role in planning, to intervene in the production of housing, and if so, housing for whom? On the proposal to provide elements of response from an exploration and restatements of French Land Tax Files, through the case of the Rennes catchment area, of which the Metropolis is known to be historically exemplary in terms of land control, without having a lot of data to measure and document it. The communication first reports on the situation of land ownership in the Rennes catchment area in 2020. 87% of the surface belongs to private actors; of the remaining 13%, about a third is owned by municipalities and intermunicipalities. This communal block property is mostly concentrated in the center of Rennes and its immediate suburbs; it is composed mainly of natural or agricultural land, then of artificial land. Secondly, we show that the areas owned by the municipal block are slightly increasing between 2009 and 2020: although transfers are numerous, they are less so than acquisitions; municipalities and intermunicipalities are therefore active on land markets. Most of the land acquired and sold goes from/to the hands of private partners, especially individuals. It is hypothesized that the intervention of the municipal block on land aims to generate housing. The third part of the communication seeks to explore this hypothesis by analyzing the contribution of the land on which a municipality or intermunicipality intervened to the overall construction effort between 2009 and 2020. Five lessons can be drawn from this: • It is mainly when they sell land, rather than when they buy or keep it, that it supports housing construction. • The communal block concentrates its effort on the construction of housing rather than businesses and industries. • About half of the social housing produced on the territory was on land on which the municipal block intervened in one way or another. • The dwellings on this type of land are mainly apartments, which testifies to a concern for densification. • The destruction of houses, apartments and businesses or industries on the acquired land shows the renewal of the urban work carried out by the communities. This communication therefore shows that the intervention of the municipal block in the land markets, in the area of ​​attraction of Rennes, is an essential factor in the production of housing, in particular social housing, in densification and urban renewal.