Xylanase, a glycoside hydrolase, is indispensable to break down xylan, a heteropolysaccharide that consists of a complex and intricate structure and constitutes the bulk of plant cell wall hemicellulose. Being the second most prolific renewable polysaccharide after cellulose, xylan consists of xylose units with attached side chains of arabinose and glucuronic acid, which leads to its heterogeneous and diverse structure. Xylanase enzymes, produced by diverse microorganisms, unlock the potential of xylan-rich biomass for industrial and environmental applications. Xylanase stands at the forefront of sustainable biotechnology, from pulp bleaching to enhancing food texture and clarity to converting agricultural waste into biofuels. This chapter gives insight into the microbial sources of xylanase, their enzymatic mechanisms, and their industrial relevance, highlighting how these natural microscopic chemists are reshaping green innovation.