The yeasts have been exploited by mankind for thousands of years for food and fermentation processes. Traditionally the yeast has been used for the production of alcoholic beverages, biomass and glycerol. Saccharomyces cerevisiae has been described as mankind’s most domesticated organism and still widely exploited yeast species in industry today. The number of yeast species described so far is about 1500 and only about a dozen is used at industrial scale. Some 70-80 species have been shown to possess potential value for biotechnology. According to modest estimate, known yeast species represent roughly 5% of the total number that may inhabitant Earth surface. Modern applications of yeasts have been greatly expanded beyond classical applications. Yeasts, especially S. cerevisiae and other non-saccharomyces yeasts today are increasingly used for the heterologous production of enzymes and pharmaceutical proteins. Yeasts have important roles in environmental applications such as bioremediation and removal of heavy metals from wastewaters. Yeasts are also used in agriculture as biocontrol agents. Several chemicals can be produced using yeast as a biocatalyst. New developments in engineering yeast have introduced novel capabilities to extend substrate range and produce new products so far yeast can not produce. S. cerevisiae is largest cultivated organism so far. Having in mind diversity and potential of all yeast species, the cultivation and utilization of Saccharomyces yeasts are still the tip of the iceberg and there is a vast potential yet to be discovered for the production of valuable products using saccharomyces and non-saccharomyces yeasts.