Arid lands have grown almost 28% since 1960 and soil fertility dropped. Mycorrhizal fungi, plants’ partners for more than 450 million years, have evolved into an organic substitute for chemical inputs. As root colonizers, they improve water, nutrient uptake and retention; are soil forming; and counterbalance the effect of drought, salinity, and pollutants. With the help of morphological and molecular methods, scientists have constructed lists of this often-invisible diversity, showing that AMF communities in arid and semiarid soils worldwide are dominated by genera of the Glomeraceae family (Glomus, Funneliformis, Rhizophagus, Claroideoglomus, and Septoglomus), even in the most stressed environments. To survive exposure to abiotic stresses (prolonged drought, extreme pH, heavy metals, organic pollutants, and high temperatures) these fungi adopt a suite of counterstrategies, including enhanced sporulation and hyphal extension, the sake of anastomosa to sustain a functional mycelium, changes in the composition of membranes and lipid stores, and activation of antioxidant (enzyme: superoxide dismutase, catalase) and protective (metabolites: trehalose, heat-shock proteins) defense systems. In the host, the mycorrhizal symbiosis activates expression of nutrient transporter and defense-related genes, reorganizes the hormonal status (abscisic acid, strigolactones) of the plant, induces accumulation of osmolytes and antioxidant enzymes, and stimulates the development of a larger root system and more stomata, allowing the highest exchange of water and nutrients. Eventually, AMF from a “microbial triad” with growth-promoting bacteria (Bacillus, Azotobacter, and Pseudomonas), which can solubilize phosphorus and fix nitrogen and produce complementary phytohormones and enzymes. This combined community improves plant tolerance of harsh conditions and supports growth in a sustainable manner under semiarid conditions.