This paper investigates the role played by the social relationships of reciprocal exchange and mutual help in the struggle for the survival of the poorest sector of urban Latin American societies, particularly in in the mexican context. I discuss the conceptual definition of the social network, the factors that are involved in its formation and permanence, and the current debate in some Latin American academic circles about the role of the social networks in the fight against poverty. Also, I present the results of research that I have carried out since the early 90s in poor urban settlements in Mexico.