Slums play many roles in city life. As the place of residence of low-cost labor, they keep the wheels of the city working in many different ways. As a first stopping point for immigrants, they provide low-cost housing that will enable the immigrants to save for their eventual absorption into society. They are adept at producing the services and commercial activities that the formal sector fails to provide through the mobilization of local enterprises and industries. Slums are extremely varied places that defy anyone’s tight definition. Many are slums because they are unrecognized by the officials of the local authority and government. This lack of recognition  informality  is both a characteristic and cause of problems of inadequacy. Slums, poverty, and they are closely related but are by no means congruent.

The story of slums is, therefore, neither heterogeneous nor coherent and homogenous. It is a story of rich variety, great achievement and typical 21st-century urban life. When more than half of the urban population lives in them, the slums become the dominant city. This is the case in many countries and needs to be recognized so that slums are awarded their rightful place in the centre of policies and politics.