About 32% of the world’s urban population live in slums. The problem of poor housing quality is overwhelmingly concentrated in the developing world. Sao Paulo has the largest slum population in South America. Here, urban poverty is concentrated in two types of housing, favelas and corticos. Favelas in Sao Paulo, unlike Rio de Janeiro, have developed fairly recently. Their rapid growth dates back to 1980 with their share of the population having jumped from 5.2% to 19.8% since then. Although both natural change and rural-urban migration have fallen significantly the housing problem remains immense.