The provision of urban services is one of the most important issues in the process of urbanization. However, more than half of the urban population in developing countries does not enjoy any of these services yet. The public sector has been unable to provide services to the ever-increasing urban population. This failure has been met by the involvement of the private sector in the provision of services: nevertheless, private services are only provided to those who can afford them. The urban poor, who are the majority of the population in urban centres, are not able to afford those services. In the absence of public and private services, the poor have managed themselves to provide services. However, the provision of services by the informal sector has been attacked by governments, which have rarely evaluated or understood this sector. This thesis investigates how the informal sector has created different networks to provide services. In order to find out how exactly this phenomenon has taken place in poor communities, an informal settlement was selected in Bogota, Colombia for a case study. Service networks were identified and classified according to their nature, the operational and technical aspects were described, and, finally, the accepted level of services by the members of the community was analyzed and inferences were drawn. In this way, the studies showed that the informal sector through the use of networks assembled by community-based organizations and/or assembled by different individuals with private initiative were successfully providing services to the poor.