Yeasts play a key role in the production of a wide range of fermented foods and beverages, with a particular focus on their ability to adapt to extreme conditions such as high salinity, low temperatures, and acidic environments. This chapter studies both conventional yeasts, such as Saccharomyces cerevisiae, and non-conventional yeasts, highlighting their contributions to the fermentation of dairy products (e.g., cheese, milk-based beverages), bread, fermented meats and fish, soy sauce, and alcoholic beverages (e.g., beer, wine). The discussion inquires into the specific yeast species involved in these processes, their metabolic activities, and their adaptation mechanisms to various stress conditions, including acidic pH, low temperatures, freeze-thaw stress (particularly in bread production), high salt concentrations, and ethanol toxicity (relevant in alcoholic beverages). These adaptations are achieved through mechanisms such as gene duplication, membrane remodeling, and the accumulation of compatible solutes like glycerol. While yeasts are beneficial in enhancing flavor, texture, probiotic properties, and preservation (especially in fermented meats and fish), they can also contribute to spoilage and the production of harmful compounds. For instance, yeasts like Brettanomyces bruxellensis can generate off-flavors, posing significant challenges to wine quality during grape juice fermentation. Important data include the dominance of Debaryomyces hansenii in fermented meats and cheeses, the critical role of Zygosaccharomyces rouxii in soy sauce production, and the use of Torulaspora delbrueckii in bread-making due to its osmotolerance and cryotolerance, making it particularly suitable for frozen doughs. Overall, this chapter focuses on the importance of yeasts in food biotechnology, showing their ability to thrive in extreme environments. It provides valuable insights into their application in improving food quality and safety, while also addressing the challenges associated with spoilage and stress adaptation.