In France, since the 2000s, weekly urban riots, and almost daily sometimes, sign accentuation so quantitative as qualitative of the ghettoization of marginalized sectors of cities. It is in particular in the complexes of the massive urbanization of the years 1950-1970, the grands ensembles d'habitat, that the phenomenon of modern ghetto can define itself. In spite of undeniable qualities of comfort and size of housing, with regard to the pre-war standards, numerous characteristics of production, populating and management engendered a defective housing environment. This one was able at first to arouse the boredom, the stress and the marginalization compared with the environment. From 1970s, increasing social tensions developed with the spatial concentration of the households most in socioeconomic difficulties. The analysis of the fate of territories of complexes in a scale wider than that of the most degraded internal sectors, as that of their little town of membership (seven studied little towns of grands ensembles), shows that the diverse aspects of the ghettoization confront under convergent forms in these sectors in spite of higher urban attributes (activities, developments and diverse equipments). The processes of material, economic, social and symbolic degradation which know these towns evoke an urban social decline, a notion from which is approached the social segregation which is a multi-form causal phenomenon. The extension of the scale of apprehension of the social degradation of spaces allows an advanced analysis, between its ideological and political frame, its social motivations and the multiplicity of its appearances, at the institutional level and the social practices. The social and urban segregation of the least qualified categories is then translated by their marginalization of the socioeconomic system, by their spatial banishment in little valued and badly managed zones, by their uneven access to the equipments of integration and social advancement as well as by the stigmatization of their housing environment and their avoidance by the superior categories, in particular of the private, in search of one to protect itself from the loss of social position. What contributes to widen the field of the social inequalities of the space, as long as the social decline of the least valued residential spaces will continue to occur because of the increase of the segregationist conducts in the urban environment.