A detailed analysis of urban segregation processes within the locality, using both quantitative and qualitative methods, reveals major social differences between neighbourhoods and even between public housing developments. Considering the case of Nanterre, a working class suburb of Paris, we exhibit a variety of socio-spatial structures which underline the social and urban complexity of the suburbs. We also show the need to take into consideration the active contribution of inhabitants themselves to segregation processes, based on the detailed knowledge they acquire of the social characteristics of different neighbourhoods or even buildings. This type of method poses serious methodological problems and requires a detailed sociological knowl...