The document is a “learning note” on financing housing for the poor. It deals with rapidly urbanizing African and Asian cities have a 15-20 year window of opportunity to meet the low income settlement challenge and create well-functioning urban areas that drive economic growth. The urban dystopia of large slums in Latin American cities can illustrate some of the worst effects of ill-managed development and have provided a laboratory for program experimentation. By 2050, the developing world will double its urban population and triple its urban area, largely through incremental and informal settlement. Demographic and migration dynamics conspire to place unprecedented burdens on cities in the global South, with the most dramatic growth occurring in secondary cities. Informal development is a rational response by urban families who have limited resources, and limited access to formal finance and housing delivery systems. Seen in a positive light, informal settlement is private investment that has outpaced public infrastructure.