In Monterrey, third city of Mexico, there exists one of the most important urban social movements in the world: the ‘posesionarios’ of the ‘colonias proletarias’. Quantitatively: they number 100 000 in a city of 1 600 000. Qualitatively: they are ideologically radical, politically conscious and realistic, mostly based on political self‐reliance. A short stay within the movement has permitted the author to grasp some non‐confidential information that should be disseminated as one of the most interesting experiences of recent urban struggles in Latin America.