Historically described through theories of marginality and urban precariousness, 'informal settlements' must disappear for Latin American cities to achieve sustainability. However, in countries such as the Dominican Republic, these neighborhoods are part of the informal market responsible for 75% of housing production. Because they powerfully shape the urban pattern of the city of Santo Domingo, a new analysis approach is necessary. For some researchers, the existence of these barrios in our cities indicates that these neighborhoods are crucial for the definition and development of contemporary urbanism. Their inhabitants are capable actors able to embrace significant transformations, particularly in terms of sustainability. In line with this approach, this article offers a study of four Dominican slums based on three categories of analysis: the inhabitant's capabilities, the compact urban structure of informal settlements, and the practice of eco-citizenship. For these purposes, a qualitative methodology was deployed using ethnographic research tools: participant observation over time and systematic description of spaces and situations. The results show that even if these informal settlements have characteristics compatible with urban sustainability, they are little recognized and dependent on internal and external socio-spatial depreciation.