The main component of biomass, cellulose, is converted into glucose with the action of an enzyme mixture of cellobiohydrolases, endoglucanases, β-glucosidases, and lytic polysaccharide monooxygenases. The obtained glucose is converted into bioethanol and other biofuels by the action of microorganisms. The degree of the biomass conversion into glucose is increased with an improvement in the properties of the enzymes; therefore, the costs of the process and the produced biofuels are reduced. Enzyme properties, such as enzyme activity under mild temperature, rather than activity and stability under high temperature, activity and stability in nonconventional media, in particular, in the presence of ionic liquids, and activity and stability under optimized pH, are required to be improved. Rational design, based on the insights into the spatial structure and catalytic function of the enzyme, is used to perform amino acid substitutions and modulate the enzyme properties. Amino acid substitutions that change the enzyme properties are also created through random mutagenesis and directed evolution. The construction of the chimeric enzymes from elements of spatial structure and parts of amino acid sequences of several enzymes allows the obtention of the enzymes with beneficial properties. The enzyme properties are also improved through a change in the spatial organization, including domain organization and glycosylation. With the application of the improved enzymes, processes of biomass conversion are made cost-effective and suitable for biofuel production.