The role of cellulase and xylanase enzymes is crucial in realizing the aim of producing ethanol (and other biofuels) and commodity bioproducts from cellulosic feedstocks. The cost of producing cellulase has been brought down significantly over the lastdecade, but it still seems to be about two to three times higher than the threshold value projected for economic production of cellulosic ethanol. We believe that the development of more effective cellulases with desirable characteristics such as high catalytic efficiency on crystalline cellulose, end-product inhibition resistance and higher thermostability shall be able to bring out a faster and more complete hydrolysis of celluloses to reducing sugars. To achieve these goals, modern tools of protein and metabolic engineering, together with process engineering and scale-up in suitable bioreactors need to be applied. This will result in the usage of decreased amounts of cellulolytic enzymes, thereby lowering their contribution to the overall production cost of ethanol and other bioproducts. Further, information on genome of the best cellulase producer, T. reesei, and its several transcriptional regulators which are involved in cellulase regulation is now available. As our understanding to modulate these regulators in response to various external stimuli increases, it is expected that it shall be possible to overproduce the desired mix of biomass-degrading cellulolytic enzymes with high yield and productivity