One consequence of Mexican agrarian reform is half of the country occupied by thousands of communities that have communal governance over their territories. However, not all communities have common land, which means that a true communal action cannot be achieved there. In the highlands of Chiapas some communities have divided their common land in individual plots, but some others have decided to keep their commons. Why has this happened considering that they share similar environment and cultural roots? Several factors contribute to explain the divergent position that communities have respect common land. One of them is demographic; communities have very different demographic growth rates, which are related to cultural and legal agreements on the access to land. Those with accords to limit the incorporation of new land users have not tended to see commons as a reserve terrain for new generations that want new plots to cultivate individually. A combination of economic and environmental characteristics explains why commons are linked to forestry use, and why this kind of land use stimulates the preservation of commons. The struggle for equality in access to land and forest resources within communities is also another factor involved in commons defence. Learning from experiences and resource scarcity are also elements implicated. All this analysis is put under the context of changes in agrarian and forestry policies in Mexico. The recent reforms to Article 27 of Mexican constitution and their possible effects on the continuity of the commons in the region are also addressed.