Isolated and poorly controlled until the end of the XIXe century, Northern Thaïland has gradually been integrated in the Thai national space following the reforms enacted during the reign of Chulalongkorn and the creation of a modem transport network. The abolition of slavery, the replacement of kind by cash for the payment of land rent have been determinant in the evolution of the Siamese social formation and have permitted the penetration of merchant capitalism in the countryside of the North. This penetration only became important after 1950 with the development of cash crops and the increasing town-country differentiation. Petty commodity production carried out by the small land bound peasantry is characteristic of most of the Northern region. But transnational financial capital is being invested in agro-industries which attempt to increasingly control the small production units. These transformations in the relations of production and of productive forces in a social formation whose dominant mode of production from « Asiatic » is becoming capitalist, have had consequences on the organization of space. To a spatial System in rings, inherited from social formations dominated by the asiatic mode of production, is substituted a spatial differentiation which is a function of the lesser or greater penetration of the capitalist mode of production. A concrete analysis of social relations in their linkages with inherited or actual social structures at the regional level is a prerequisite to any criticism of land planning.