A significant status in the formation and maintenance of soil fertility is held by microorganisms that can reliably provide the assessment of the health and quality of the soil. Soil microorganisms have been applied in agriculture as biofertilizers and biopesticides as well as phytoremediation agents. Microbial cooperation in the rhizosphere is essential for the sustainability of soil fertility and plant growth. Plant-growth-promoting microorganisms (PGPM) are defined as soil-borne bacteria, fungi and yeasts with plant promotion or protection activities. Positive outcomes of PGP microbe’s application are enhancement of seedlings emergence, faster plant growth, higher biomass production, increase of root length, and branching, increased leaf area, and chlorophyll content, and higher resistance to abiotic stresses as well as to pests or diseases. The total soil yeast count is usually relatively low as compared with the number of bacteria and filamentous fungi. Yeasts are important as a source of food for other soil microorganisms, they participate in the cycling of matter in soil, and are involved in the formation of the soil mechanical structure. Some yeasts’ strains are recognized as PGP microbes, with ability to produce indole-3-acetic acid (IAA), siderophores, to stimulate mycorrhizal-root colonization, pathogen inhibition and phosphate solubilization. Several genera of soil yeasts, such as Candida, Geotrichum and Rhodotorula were positive to in vitro P solubilization tests. Representatives of Candida, Geotrichum, Rhodotorula, Saccharomyces, and Williopsis are able to nitrify ammonium to nitrate via nitrite in vitro. Also, yeasts exert biocontrol against fungal phytopathogens indirectly, by competing for space and nutrients, modifying the environmental conditions (pH), or promoting plant growth and plant defensive mechanisms with inducing plant systemic resistance to pathogens and antibiosis. Literature data claim that soli yeasts can find its use in sustainable agriculture.