As the world population grows and cities have become the centre of human activity, urban life has become one of the most important objects of study for the social sciences. One of the main societal discussions is about the presence of increasingly fortified residential enclaves. In Mexican cities, these exclusionary places have burgeoned since the 1990s. However, despite the often very trenchant critique of these spaces in much research, this criticism has by no means hindered their proliferation, which highlights the disconnect between academic work and applied practices in planning, urban design, and real estate development. This chapter presents some of the key discussions regarding urban life and social interaction, as well as related exclusionary practices. The focus here is very much on urban fragmentation rather than socio-spatial segregation, which has tended to dominate the academic discussion because the concept refers to both the tangible and intangible borders and boundaries that affect social interaction in the city. Urban fragmentation has been associated with the increasing presence of physical barriers, walls, buffer zones, and other design elements that have had the effect of breaking up the core sense of the city as a more or less unified public whole and a space accessible to all. The chapter also discusses the privatisation of public life, which is a much richer concept than the privatisation of public space, as it transcends the tenure, use, or physical configuration of urban space and can help us understand how people live in the city and how this affects interaction. The focus on planning practice, urban fragmentation, and privatisation of public life is presented to highlight the increasing impact of exclusionary urban configurations on people's everyday lives.