Under the 1917 constitution ejido land was collectively held and inalienable, so Mexican cities expanded largely through illegal sales of ejido plots later regularised by CORETT. The 1992 reform ended land redistribution and allowed ejidos to certify individual parcels through PROCEDE, to enter joint ventures with developers and, by qualified assembly vote, to convert parcels to full private ownership and sell them. Roughly half the national territory, and much of the land ringing every large Mexican city, was held in ejidos and comunidades.
The reform legalised the land market on which Mexican urbanisation had in fact always run, turning the peri-urban ejido from an object of clandestine subdivision into a formal supply of development land. It enabled the mass privately built housing estates of the 1990s and 2000s while leaving informal growth intact, since certification and conversion proved slower and more contested than the market that preceded them.
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