Biofuel derived from lignocellulosic biomass has attracted considerable attention as a renewable energy source. Nevertheless, the conversion of lignocellulose into fermentable sugars is inherently difficult because of the complex structures of lignocelluloses. Accessory proteins, like expansins, have a non-hydrolytic disruptive effect on crystalline cellulose and can synergistically cooperate with cellulase to improve hydrolysis efficiency. This review summarizes recent studies on expansins and expansin-like proteins, in terms of their expression and purification, synergism in lignocellulose hydrolysis, structure-function studies and binding characteristics. Future research prospects are also presented. This review provides a discussion of expansins in the context of lignocellulose hydrolysis.