Interest in hemicellulolytic enzymes has increased remarkably during recent years. This is mainly due to the new areas of application of these enzymes within the pulp and paper industry. Among these, the most promising seems to be utilization of hemicellulases, especially xylanases, to increase the bleachability of kraft pulps. This is partly due to the great potential of an environmentally safe method. The main enzymes needed in the enzyme-aided bleaching have been shown to belong to the group of endo-beta-xylanases. Xylanases act mainly on the relocated, reprecipitated xylan on the surface of the pulp fibres. Enzymatic hydrolysis of this specific type of xylan renders the structure of the fibres more permeable, allowing enhanced extraction of residual lignin from the fibres. The hydrolysis of hemicelluloses in the inner fibre layers may also enhance the bleachability. The main goals in the enzyme-aided bleaching of kraft pulps have been the reduction of consumption of chlorine chemicals in the bleaching process, and consequent lowering of the AOX of the effluents. In the production of totally clorine-free pulps, enzymes have also been successfully used for increasing the brightness of pulp. Other suggested enzymatic modifications of fibres are aimed at improved drainage (water removal) in the paper machine, improvement of fibre properties or production of dissolving pulps. The xylanolytic enzymes and their application areas are reviewed.