This paper explores the meaning of the concept of informality as applied to the waste management sector, by presenting the case of municipal waste collection in a neighbourhood of Mexico City called Tepito. Tepito's municipal service of waste collection is intricately related to informal activities of waste collection and management. This paper focuses on the work of informal street sweepers, who collect waste in certain streets of the neighbourhood, replacing the municipal collection service; and on that of "volunteers", unwaged informal workers recruited by the garbage-men to help on the municipal collection route. The informal cash flows resulting from the work of the volunteers are also described. The case of Tepito illustrates two formal-informal arrangements in the provision of the waste collection service: the coordination of independent services, and a relation of interdependence where the formal system is sustained by informal work. By exploring the scale of informality, the actors involved, and its governance system, this paper suggests that informality exists not as a particular sector of waste management, but rather as unregulated practices carried out by governmental and non-governmental actors, which are enabled by an informal governance system, and which (in Tepito) play a crucial role in sustaining the municipal waste collection service. As different systems of service provision are co-constructed by both formal and informal elements, informality may best be identified at the level of practices that occur within such systems. Conclusions discuss policy implications and avenues for future research.