People in third world and developing countries are suffering from menace of protein deficiency in their diets resulting in serious protein malnutrition problems. The situation, accompanied with rapid population growth demands exploration of new & un-conventional protein sources to fortify human foods. Saccharomyces cerevisiae is very promising and cost effective source of single cell protein due to its bigger size, easy harvesting, lower amount of nucleic acids and good blend of essential amino acids. Its protein quality & chemical score is comparable with soybean or egg protein. The yeast is highly significant as an alternative source of protein to cover the increasing demands due to rapidly escalating population. This book emphasizes on production of cost effective yeast, its evaluation as protein source and its behavior in various food formulations to improve functionality and protein quality of finished products. The book is especially valuable for professionals, and researchers working in area of Food Technology and Human Nutrition.