Territory was analysed as the expression of social organisation in spatial terms. Characterised by particular patterns of behaviour and attitudes, territorial organisation of outdoor residential environments is investigated as defined by the patterns of functional activity and the behavioural types of socialisation occurring in each space as well as the dwellers' attribution of territory regarding each space category. Territorial definition and residents' perception of space definition are discussed as a means of affecting residents' sense of community, security, sense of place and control, and the overall maintenance of the site. The degree of social definition of space was assessed through the investigation of territorial behaviours in semi-public, semi-private and private outdoor spaces of two low-income housing schemes (Brazil). Results show that residents tended to reinforce or modify the physical definition of spaces, either by developing strategies to clarify space definition and to make apparent who was responsible for what space, or by creating categories of social spaces which had not been suggested by design. It was found that the common semi-public or semi-private spaces, when indicated by design, may not correspond to what residents perceive as their semi-public or semi-private territories. The more intelligible territories were, the better spaces were socially defined.