Lignocellulosic wastes has been widely discussed as a promising natural chemical source and alternative feedstock for second-generation biofuels. However, there are still many technical and economic challenges facing its utilization. Lignin is one of the components of lignocellulosic biomass, and is the most rigid constituent and can be considered as a glue providing the cell wall with stiffness and the plant tissue with compressive strength. In addition, it provides resistance to chemical and physical damage. Resistance of lignocelluloses to hydrolysis is mainly from the protection of cellulose by lignin and cellulose binding to hemicellulose. The present book provides basic knowledge and recent research on different applications of biomass, focusing on the bioenergy and different pretreatment methods that overcome the aforementioned hurdles.