Population Patterns and Household Trajectories in the Residential Milieu: the Example of the Seine-Saint-Denis This article examines the processes underlying changes in the residential population of the Seine-Saint-Denis department (a suburban district to the north and east of Paris, containing 500,000 households) from three points of view: 1) the residential logics of different social groups, 2) the effects of the housing supply structure and 3) of the social markers attributed to the different local areas. Data from the 1990 Census are used to establish housing categories containing housing types whose residents have similar characteristics. These categories are then ranked and interpreted using an index of socio-residential status, whose spatial variations indicate the influence of the social markers of the communes on the population (residential areas), which can derive from the composition of their housing stock (housing zones) or from their geographical situation (local effects). These typologies are then used to interpret the residential mobility of households who moved into a dwelling in the Seine-Saint-Denis in 1994. Data pertaining to the 1,568 surveyed households are analysed in three ways: to determine the residential trajectories of households; to shed light on the locational choices of households, and on the scope for action and constraints shaping their decision; and current residential histories are used as an indicator of changes in local populations.