The concept of sustainability is usually defined according to specific socioeconomic contexts and is vague in application, but nevertheless essential for defining longterm objectives. This work seeks to demonstrate that the place of sustainability in a development model depends on the cultural values behind abstract ideas and on the perceptions and interests of different social and political groups regarding the environment more than it does on the biophysical exchanges between societies and the natural environment. The idea of sustainable development reflects a new political will to continue to live on earth in the same fashion as at present, but new forms on international organization, government, and commerce more conducive to sustainable development have not yet clearly emerged. Other concepts used in social and anthropological analysis, such as social reproduction, appear relevant in considering sustainability. Sustainable development should be analyzed and applied at both the macroeconomic and microeconomic levels. Demographic growth is a determining factor in use of natural resources in today's world, but its dysfunctionality at the macro level contrasts with its continuing functionality at the family level in many poor rural communities. An exploratory analysis of the living conditions of the natives of the tropical forest of southeast Mexico, the Lacandon, suggests how different populations understand the concept of sustainability and manage their vital resources accordingly. The Lacandon tropical forest of 1.4 million hectares had lost only 6% of its original cover through the early 1960s. But beginning in 1963, the Mexican government, as part of the Alliance for Progress program, began a colonization project that eventually led to disorganized migration and uncontrolled harvesting of tropical woods in the forests of Chiapas. A settlement program begun in the area nearest the Guatemalan border to control the movements of Guatemalan refugees and guerillas in the area led to massive deforestation. Although deforestation in the Lacandon forest has been prohibited, it continues to occur as new arrivals hoping for quick profits harvest anything of value they find. The major groups involved in the preservation or destruction of the Lacandon forest were the Indian and mestizo inhabitants, the opportunists in search of quick wealth, cattle ranchers, functionaires, and the urban populations of nearby Palenque. Although all groups believed that the forest had been created by a God, they differed as to its purpose. Some felt it existed to be exploited by humans in whatever fashion they desired, others felt a responsibility to protect the forest and its life. The natives appeared to have a more "sustainable" ideal of ecological protection, but in fact their rapid population growth represented an acute threat to the forest's resources.