The assimilation process of immigrants is in part an urban issue involving housing patterns, participation in community life, the use of public service etc. How is the urban presence of immigrants reflected in the use of public space and what kind of specific social dynamic is emerging in this kind of space - a space which is in principle universally accessible? Does it encourage social cohesion, as many urban planners believe, or does its use reflect the loosening of social bonds, as some social scientists argue? In order to discuss these issues, we present the results of a study carried out in six neighbourhoods of the metropolitan region of Montréal, selected for there multiethnicity (in terms of numbers and of ethnocultural diversity), for their location (in the centre and in the periphery), and for their socioeconomic profiles (middle class suburb, low-income enclave, old socially heterogeneous neighbourhood). In each neighbourhood, we conducted interviews with key informants from about 15 local associations (sometimes perceptive observers of the social life of the neighbourhood). We made systematic observations of the sociability of the main public places (parks, metro [underground] station, shopping centre, café etc.) and conducted brief interviews with the users of these places. In this paper we will mainly discuss issues such as social segmentation of space and patterns of cohabitation by types of users, as well as the different connotations of the concept of appropriation.