Xylanase (Endo-1, 4-?-D-xylan, xylanohydrolase, EC 18.104.22.168) is an important xylan degrading enzyme involved in the random cleavage of xylan to produce xylose, xylobiose and xylo-oligosaccharides. It is predominantly present in microbes and plants. This enzyme has been studied more extensively from fungal and bacterial sources and produced commercially. Its commercial applications in biobleaching paper pulp and increasing pulp brightness, biofueling, improving animal feed, bread making industry, fruit juice clarification are well known. The molecular structure and hydrolytic pattern of xylanases have been reported extensively and the mechanism of hydrolysis has also been proposed. The gene encoding the enzyme has been cloned with the objectives of overproducing the enzyme and altering its properties to suit commercial applications. In this review we have discussed its structural, physicochemical and molecular characteristics. Besides, commercial applications and biotechnological exploitation of the enzyme have also been described.