This article is aimed at defining the role of migratory movements in the dynamics of the sociodemographic transformation of neighbourhoods in the Brussels-Capital Region, and at making some observations in terms of political implications. There are several significant summarising elements which may be drawn from this analysis of complex migratory movements in the Region. The poorest territories in the city – the “poor area” – are at the crossroads of diverging migratory movements, marked in particular by the arrival of new immigrants from poor or intermediate countries and the departure of resident populations. Nevertheless, the analysis also shows that these neighbourhoods may not be reduced to having a transit function, given that a significant proportion of their population remains there. In contrast, the richest parts of the city, located in the southeast quadrant of the Region, have experienced much less massive migratory movements. They are not home to newcomers or to households leaving the disadvantaged areas of the city. They thus appear to be closed for the most part to population movements.