Fermentation is being used since ages as a safe technique for food preservation and uses minimal resources. Most common fermentations are alcohol fermentation, lactic acid (homofermentation), lactic acid (heterofermentation), butyric acid, mixed acid, propionic acid and acetic acid. The protein industry uses fermentation in three primary ways, 1) Traditional fermentation, 2) Biomass fermentation, 3) Precision fermentation: uses microbial hosts as cell factories for producing specific functional ingredients that typically need greater purity than the primary protein ingredients and are incorporated at lower levels. This book is aimed to both introduce and survey the fermentation technology and its relationship with functional foods, as well as, investigate and inspect different research progresses of protein factory-microbial fermentation technology.