This paper focuses on the implications of the practice of Judaism in the use of the urban space. It takes the example of the construction of eruv, a ritual system of temporary shifting of the public-private boundaries in Parisian buildings inhabited by observant Jewish families. Because it represents a ritualization of the link between a religious community and the residential space, the eruv calls into question the role of religion in the production of social and spatial boundaries. If it symbolizes the presence of a Jewish community, it also reveals its internal diversity, between religious divisions and continuity, and the boundaries between residential proximity and community construction.