This chapter discusses the ethanol production process by fermentation, with general information about the chemical ethanol specie, the ethanol industry in Brazil, history of ethanol fermentation, ethanol production data in Brazil and the United States. Production processes are described, raw materials used (sugarcane and molasses are practically the only used in Brazil), microorganisms used in the fermentation process, preparation and correction of fermentation media (must). The ways of conducting the fermentation process are presented, with emphasis on Melle-Boinot process (about 70% of ethanol production in Brazil) and in the continuous process (remaining 30%) and in the process with immobilized cells on inert supports (with information stalks of cane sugar and corn cobs media as yeast for production of ethanol). Finally, are discussedthe physical and chemical factors that influence the metabolism of ethanol producing yeast and their controls of ethanol fermentation.