Biocrusts are multifunctional elements in deserts that have been widely studied in Australia, China, and the USA. However, biocrust research in Mexico have also increased in the last two decades. Mexico has deserts (Chihuahuan and Sonoran) and semideserts (Querétaro and Tehuacán) with particular environmental characteristics that likely have different effects on biocrust structure and function. We synthesize studies on biocrusts performed in Mexican deserts and semideserts in the last 24 years to describe their species composition, ecology, and ecosystem function, and to identify new lines of research. Biocrusts are composed by 52 genera and 148 species of algae, fungi, cyanobacteria, lichens, and mosses, some of which are new records for biocrust diversity worldwide. Biocrust composition and distribution is determined by soil properties, vegetation cover, and geological history. However, biocrusts in the Tehuacán semidesert differ in their composition from biocrusts in other Mexican and American deserts. Biocrusts have opposite effects on germination, seedling survival and growth, and on soil invertebrate diversity. Moreover, biocrusts have opposite effects on infiltration, although biocrusts increase soil stability. Biocrusts contribute to soil nutrient dynamics and may form fertility mantles that regulate soil fertility. However, grazing, rainfed agriculture, and firewood extraction alter biocrust structure and function. Even though biocrusts are essential in the Mexican deserts and semideserts, there are still information gaps in the understanding of biocrusts such as the biological conservation of biocrust species, the utility of biocrusts to restore degraded soils, and the effect of global change on the structure and function of biocrusts. Keywords: Biological soil crusts; Germination and seedling survival; Infiltration rate and soil stability; Soil C and N dynamics; Xeric shrubland.