The chapter introduces xylan as a major component of plant hemicellulose. It is the most abundant renewable polysaccharide in nature after cellulose. The chapter describes its structure and its interaction with plant cell walls. Due to the complex structure of xylans, several different enzymes are needed for their enzymatic degradation and modification. Properties and production of different enzymes—namely, xylanases, β-Xylosidases, α-Arabinosidases, α-Glucuronidases, and esterases are discussed in the chapter. Application of xylanases in pulp and paper making is reviewed in the chapter. The process involves some steps: prebleaching of kraft pulps, enzymatic debarking, fiber modification, production of dissolving pulp, removal of shives, and retting of flax fibers. The potential for use of xylanolytic enzymes in the food and feed industries is also high. The main aim in the application of xylanolytic enzymes is the hydrolysis of hemicellulosic substrate for production of fermentable sugars. The knowledge gathered on the hydrolysis mechanism of hemicelluloses, especially xylans, is greatly promoted the rapid application of these enzymes in new areas. Attention is focused on recent advances and on several aspects that were not covered in earlier reviews.