Slum dwellers in these countries often lack improved water sources, improved sanitation facilities, durable housing, sufficient living area or a combination of these four characteristics that now define ‘slums’. Improving the lives of the urban poor will therefore require large, multisectoral investments. Based on the experience of successful countries, a number of factors have been identified as prerequisites for meeting the slum reduction target at the national level: appropriate policies, access to basic services, security of land tenure, and harmonization of the definition of slums and methods for monitoring and evaluating them.