J.F. Martínez-Montoya, J. Herrero-Isern, J. Aceves-de Alba, J. Palacio-Núñez, V.M. Ruiz-Vera, and G. Olmos-Oropeza. 2012. Approximation of the surface of gypseous soils in San Luis Potosí, Mexico. Cien. Inv. Agr. 39(3): 545-556. The gypseous soils of San Luis Potosí State, México, are not well map-delimited, despite their broad extent and the specific agricultural and environmental management they require. The present article highlights the location and extent of the gypseous lands in the Altiplano and Zona Media of San Luis Potosí State. For this purpose, soil, geology and vegetation maps as well as studies related to gypsum-rich soils, aerial photographs, and satellite maps (termed ‘espaciomapas’ in Spanish, these refer to Landsat-5 Thematic Mapper images of Red-Green-Blue:432 composition printed at 1:250,000 scale) were reviewed. Additionally, field and laboratory work were carried out. The maps provided by the Commission for Studies of the National Territory (CETENAL) proved very useful during the mapping process, especially as an initial reference to the presence of this soil type. The gypseous surface extent (397,258 ha) delineated in this study is double that (193,907 ha) reported in the CETENAL cartography at 1:50,000 scale. Moreover, areas with shallow gypsum, i.e., a gypseous horizon occurring at a depth of less than 50 cm, were discriminated from areas with deep gypsum (termed shallow and deep gypsum phases, respectively). This distinction between shallow and deep gypsum phases is very useful for resource management planning. The maps produced serve as a reference for specific studies aimed at evaluating the suitability of land for production or environmental purposes at large scales, in which case more detailed mapping will be required.