This article aims to construct a conceptual model of the “support” phenomenon reported by Mexican mothers in a marginalized area of Mexico City.Through an extensive literature review, the authors´ten years of experience in the area and four focus groups we found that the “support” reported by the participants displays common features with the concept of exchange networks studied by social anthropology and with the concept of social support from social psychology.The “support” reported by the participants differs from the concept of social support in the function that it performs of contributing to survival in conditions of urban poverty and social exclusion. The contribution of “support” to survival is the concept´s core category form which three dimensions stem: a) willingness to break social norms if an act of support demands it b) unbreakable family loyalty bound by obligation, and c) the mother as the principal source of authority.