PIP: It is argued that mechanisms for planning land use and controlling urban expansion in Mexico City have failed to achieve their aims. Although in theory Mexico's urban planning process has recently attempted to go beyond purely physical aspects to include socioeconomic dimensions, it has in fact been inflexible and oriented to exclusively to technical and administrative aspects, to the detriment of social distribution goals. Planning instruments have not included important aspects such as specific mechanisms for altering employment structures or income levels or mechanisms for providing access to land or housing to the most disadvantaged groups. The urban planning process in Mexico City, instead of assuming a socially compensatory role in favor of disadvantaged groups, has maintained the status quo or discriminated in favor of the already advantaged. The spatial and technical orientation or urban planning in Mexico City does not leave room for a well-defined social policy. The population of the Mexico City metropolitan Zone increased from 3 million in 1950 to 18 million in 1985, while its total area increased from 11,750 hectares in 1940 to 125,000 in 1985. Transfer of population from the Federal District to the conurban municipios of the state of Mexico has been very significant since the 1970s. Around 20% of the total area of metropolitan Mexico City has been settled through illegal means, with communal and ejido lands accounting for a large share. Settlements on some 60% of lands in metroplitan Mexico City were illegal or irregular at some time. Low income housing is the cheapest form for the government because the frequently illegal status of settlers prevents them from making any demands for services or equipment for the 1st several years. Construction is undertaken and financed almost entirely by the settlers themselves, freeing the government of responsibility in regard to the constitutionally mandated right of all Mexicans to housing. The Urban Development Plan of the state of Mexico published in 1986 proposed 2 important programs for controlling urban growth. The territorial reserves program aimed to anticipate the need and make available through purchase, expropriation, or other means sufficient lands for housing to which the lowest income groups would share access. The "Paint Your Line" program establiished physical limits for urban expansion in each of the 17 conurban municipios in the State of Mexico. To date, however, few lands have been set aside for legal acquisition and the Paint Your Line program has been slow in delimiting the areas to be settled. Data from a 1989 study in the municipios of Chalco and Ixtapaluca demonstrate the shortcomings of the programs, which do not address the true processes and agents that control new settlements and especially illegal occupations and which fail to satisfy the needs of low-income population sectors.