Cities, large and small, are at the heart of a fast changing global economy – they are a cause of, and a response to world economic growth. Many urban areas are growing because their rural hinterlands are depressed, which forces impoverished rural people to move to the cities in search of work. These newcomers often end up not finding the opportunities they are looking for, so they become part of the urban poor. Upon arrival to the city, they often encounter lack of housing and infrastructure services. To make up for the lack of available homes, newcomers often set up shelters on the city outskirts, usually on public-owned land. They often live without electricity, running water, a sewerage system, roads and other urban services. In addition to dealing with poor sanitation and pollution from dirty cooking fuels and primitive stoves, they are exposed to modern environmental hazards, such as urban air pollution, exhaust fumes and industrial pollution.