Currently, bioethanol is the most promising alternative renewable energy source to fossil fuels. Bioethanol has the potential to provide sustainable, cost effective energy while reducing greenhouse gas emissions. The complex lignin-cellulosehemicellulose matrix of the biomass has to be fractioned and the carbohydrate polymers need to undergo hydrolysis to yield fermentable sugars. This hydrolysis step is typically catalyzed by cocktails of enzymes including cellulases, hemicellulases and other accessory proteins that target and degrade specific constituents of cell wall. The requirements of enzyme complexes which act synergistically to unlock and saccharify polysaccharides from the lignocellulose complex to fermentable sugars represent major costs in the overall process and present a great challenge. Hence, improvements in the development of economically viable technologies for the production of saccharifying enzymes are essential for optimizing the biofuel production process. Topics are summarized from a practical point of view including classification and properties of cellulases, synergistic action, action mechanisms and accessory proteins as well as the future trends for cellulase production, applications and biotechnological perspectives of these enzymes.