This chapter discusses foodborne yeasts. Yeasts are undoubtedly the most important microorganisms exploited by mankind. A variety of other metabolic products of yeasts have been used commercially, and the whole cell mass is also produced in large quantities for baker's yeast and fodder yeast. With the advent of modern biotechnology, newer methods for the exploitation of yeasts have been developed. The disadvantages yeasts present to humans are of secondary importance. Only few species can be considered as human pathogens, and none of them is known to cause food intoxication. Subsequently, yeasts normally play a small role in spoilage; however, conditions favorable to their growth can be a major factor in deterioration and may cause great economic loss. The chapter updates the state of knowledge on the ecology of food spoilage yeasts and the methods of studying them. The role of yeasts in food spoilage is also discussed.