Extremophilic and extremotolerant yeasts are unicellular or dimorphic fungi from the Ascomycota and Basidiomycota lineages that can thrive in harsh environments. Their ability to grow under conditions such as extreme temperatures, salinity, osmolarity, pH, UV radiation, and chemical stress makes them valuable for diverse biotechnological applications. Many of these yeasts can metabolize a broad range of substrates, including agro-industrial waste, which supports their use in the sustainable production of biofuels, oleochemicals, enzymes, and other high-value bioproducts. Their metabolic versatility also positions them as promising candidates for ​​bioremediation of pollutants such as heavy metals and hydrocarbons. In the food and beverage industry, novel yeast strains have been identified that tolerate osmotic and acidic stress during fermentation. Furthermore, certain species are capable of synthesizing carotenoids and other bioactive compounds under extreme stress conditions. Although still under development, yeast-derived bioproducts have the potential to transform the energy, environmental, food, cosmetic, and pharmaceutical sectors, contributing to a greener economy. This chapter explores the adaptive strategies and biotechnological potential of yeasts inhabiting extreme environments, highlighting their emerging role in sustainable industrial innovation.