Technical Abstract: Microbiological spoilage of foods and beverages is caused by a wide variety of bacteria, molds and yeasts. Yeast growth is favored by low pH, generally 5.5 or lower, and by the presence of sugars, organic acids and other easily metabolized carbon sources. Yeast spoilage is often manifested by growth on the surface of products such as cheeses and meats and by fermentation of sugars in liquid and semi-liquid products. Food and beverage spoilage yeasts include a relatively large number of species representing both ascomycetes and basidiomycetes. With the ever increasing variety of consumer products and the need to preserve flavor and texture through minimum processing, susceptibility to spoilage has increased, as has the diversity of spoilage species Molecular comparisons have provided an understanding of yeast phylogeny that was not possible from analyses of morphology and physiology. Gene sequence determinations have also provided a rapid, accurate means for identification of individual species. Sequencing of species-diagnostic genes represents the most accurate means for strain identification and several rapid identification methods using molecular probes based on these sequences have been developed and are becoming available to food microbiology laboratories. In this chapter, methods for yeast identification using conventional as well as molecular methods will be discussed.