Xylanase, an enzyme that degrades xylan, a major component of lignocellulosic biomass, has emerged as a powerful tool in waste treatment and environmental remediation. This chapter provides a comprehensive overview of xylanase, including its definition, types (endo- and exo-xylanases), and enzymatic mechanisms. The various microbial sources of xylanase such as fungi, bacteria and yeasts will be discussed with respect to the factors influencing its activity. The methods of xylanase production, purification and characterization will be reviewed along with their relative importance for industrial application in maximizing enzyme efficiency. This chapter indicates the various uses of xylanase in agricultural, pulp and paper and food-processing waste treatment and its possible role as an environmental pollutant reducer in terms of chemicals and organic waste. The environmental benefits of xylanase include soil remediation, pesticide degradation, and removal of heavy metals and spilling oil. Case studies are there to show practical use of xylanase in wastewater treatment plants and show how it is effective in the real world. If these potential applications are exciting, they will throw up problems such as enzyme stability, cost of production and substrate specificity. The chapter ends with perspectives on future innovations and directions, including enzyme engineering, hybrid enzyme systems and integration of xylanase to circular economy models. Xylanase is undoubtedly emerging as a suitable solution to sustainable waste management and environmental rehabilitation.