Abstract
The emergence and growth of unauthorized settlements in the cities of the developing world are discussed and an outline is given of typical aspects of living conditions there. Recent trends in policy towards legalization and improvement are also presented and the possible implications these policies may have for meeting the shelter needs of the urban poor are debated. The main argument is that due to the heterogeneity of unauthorized settlements, in origin and composition as well as in a political and institutional context, upgrading interventions face a variety of challenges and may have outcomes that are not necessarily beneficial for the poorest.