We'll analyze some of the main urban changes taking place in contemporary society. First of all, the correlation industrialization-urbanization and the shift from the so called 'industrial'city' to metropolitan systems. Social effects of the urban sprawl. The loss of public spaces and their privatization. The militarization of the cities. Social and etical responsabilities of architects and planners in the new design of cities like fortresses. Participatory planning: children as indicators of urban well-being and as planners.