In the past decade, a century of debate over whether termites produce their own cellulases has been resolved by the application of molecular genetic techniques. Cellulase genes were present in ancient bilaterian animals, and have been passed down to termites and many other invertebrate lineages over several hundred million years. Termites contain multiple endoglucanase gene copies, all of which come from glycosyl hydrolase family 9, but the roles of the different gene copies are not yet clear. Enzyme assays and RNAi experiments indicate that endogenous cellulases play a key role in termite metabolism. The overall contribution of these enzymes in members of the Termitidae (which lack cellulolytic flagellates) appears to be greater than in members of other families. A major shift in the site of expression of endoglucanases and β-glucosidases from the salivary glands to the midgut has occurred in some members of the speciose family Termitidae. Investigations into the roles of different members of the termite colony in digesting cellulose have begun, and have revealed major variations in the level of expression, including differences between different sized workers. In fungus-growers and soil-feeders, endogenous cellulases appear to be of relatively minor importance, but have nonetheless been retained in the genome.