The cellulosic Biomass has became a interesting product to be used like raw material for biofuels productioning, ethanol specially. The critic step on its convertion into ethanol imply polysaccharides degradation to fermentable sugars, process that is called saccharification. The cellulose, biomass principal component, is hard to be degradeted in mild conditions. More resent researches have been focused on some kind of pretreatment of biomass o cellulose in order to obtain easy to degrade materials to fermentable sugars. This paper shows the outstanding pretreatments of cellulose and biomass for converting it, into fermentable products using ethanolic pathway.