Yeasts are, without doubt, both quantitatively and economically, the most important group of microorganisms exploited by man. The yeast production is one of the largest fermentation industries, which is considered to be one of the oldest products of industrial microbiology. The chief industrial applications are brewing, baking. Feeding of humans and animals as a form of single cell protein (SCP) and the production of many compounds. Commercial yeast production includes distiller's yeast; wine yeast, brewer's yeast, baker's yeast, single-cell protein (SCP), food and fodder yeast, production of yeast extract, medicinal yeast and genetically engineered production from yeast will be discussed. With recent developments are biotechnology and genetic engineering, a second generation of value added to yeast-derived products is emerging. These new techniques are also adding unprecedented scope and precision to the efforts to modify yeasts in order to increase their usefulness. It is hoped that these developments will result in major advances in such areas as food and nutrition, health care and industrial chemistry in the future.