Trichoderma reesei is the anamorph of ascomycete Hypocrea jecorina, and known to be a cellulase and hemicellulases producer. While long believed to be asexual, it was recently discovered that it also perform sexual reproduction, meaning T. reesei is heterothallic. Heterothallic species require two compatible mating partners each of them carrying a different mating type locus--either MAT1 -1 or MAT1 -2 --which are required for successful sexual reproduction. Originally, T. reesei isolate QM6a was isolated from the Solomon Islands during World War II due to its ability to degrade canvas and garments of the US army. Recent advances in the biochemistry of cellulase enzymology, the mechanism of cellulose hydrolysis (cellulolysis), strain improvement, molecular cloning and process engineering are bringing T. reesei cellulases closer to being a commercially viable route to cellulose hydrolysis. Several industrially useful strains have been developed and characterised, e.g. Rut-C30, RL-P37 and MCG-80.