The interest in alternative fuels has been increasing worldwide due to reasons such asthe negative effects of fossil fuels on the environment, global warming, the significantdecrease in energy demand in the world and negative conditions in the oil market. Thefeatures of alternative fuels such as significantly reducing greenhouse gas emissions,meeting the worldwide need for raw materials and being able to be produced fromrenewable raw materials make these types of fuels attractive. Bioethanol, a regular fuelform, is regarded as the one of these alternative fuels and is the most prevalently usedfuel type. Ethanol, whose chemical formula is C2H5OH, is a flammable, clear, colorlessand slightly toxic chemical compound. It can be produced from petrochemical rawmaterials by acid-catalyzed ethene hydration or from various raw materials byfermentation. Fermentation processes occur with the use of microorganisms such asbacteria, yeast and filamentous fungi. Both yeasts and bacteria are able to efficientlyconvert sugars to ethanol through fermentation processes. The gram-negative bacteriaZymomonas mobilis and the yeast Saccharomyces cerevisiae are reported as the mostused microorganisms for bioethanol production. In order to make ethanol productionmore economical, low-cost organic wastes or byproducts such as molasses, whey,starch, fruit peels and cellulosic materials are suggested to be used as carbon sourceand/or complex substrates in the fermentation medium.Keywords: Ethanol, Fermentation, Zymomonas mobilis, Saccharomyces cerevisiae