Fermented foods and beverages have been an important part of our lives in all over the world. Their production is one of the oldest manufacturing and preservation methods, dating back to ancient times. Yeasts, mainly Saccharomyces cerevisiae, and lactic acid bacteria have long been used for the production of many fermented products. In food industry, yeasts have an important role in the production of alcoholic beverages, bioethanol, baker’s yeast and yeast-derived products. Lactic acid bacteria also have a fundamental effect on the production of some food products such as yoghurt, fermented vegetables, sour-dough bread and others. This chapter gives some information on the beneficial aspects of yeasts and lactic acid bacteria in foods and beverages.