Many investigators offer direct fermentation of starch using amylolytic microorganisms as an alternative to the conventional multistage that employs commercial amylases for liquefaction and saccharification, and followed by yeast fermentation. By using the amylolytic microorganism, ethanol production cost can be reduced via recycling some of the microorganism back to fermentors, thereby maintaining a high cell density, which facilitates rapid conversion of sugar into ethanol. However, there are very few types of amylolytic yeasts that are capable of efficiently hydrolyzing starch. Recombinant microbes and mix of amylolytic microorganism with glucose fermenting yeast in co-culture fermentation can resolve this setback. To further minimize contaminations and process handling cost, a single step or direct bioconversion of cassava or tapioca starch to bioethanol in one reactor (i. e. simultaneously saccharification and fermentation) in place of separate multistage processes will be focused upon in this chapter.