Degradation of cellulose represents a key step for efficient generation of biofuels such as ethanol or butanol from non-food crops. Several strategies aim to improve the performance of cellulases in order to make the overall process more cost-efficient. In one strategy, novel arrangements of cellulases are developed. The resulting so-called designer cellulosomes might allow equipping fermenting hosts with sufficient cellulase activity to grow on cellulose as sole carbon source and, thus, enable consolidated bioprocessing. Other strategies aim to engineer cellulases with higher thermostability and activity to make cellulose hydrolysis more efficient. Current developments in the field of cellulose engineering are summarized and achievements as well as limitations are highlighted.