Lignocellulosic biomass (LCB), including agricultural residues, forestry by-products, and food processing waste, is a renewable and abundant resource with high potential for sustainable valorization. Rich in cellulose, hemicellulose, and lignin, it can be converted into a variety of value-added products, including bioethanol, biomethane, organic acids, enzymes, bioplastics, antioxidants, and bio-based materials. Technological advances in pretreatment, enzymatic hydrolysis, and microbial conversion have enhanced the efficiency of these processes, helping overcome challenges, such as biomass recalcitrance and low product yields. Integrated biorefineries and circular economy approaches further support the full utilization of lignocellulosic waste, reducing environmental impact while generating economic value. This chapter discusses recent progress in lignocellulosic biomass valorization and its role in sustainable biorefineries and circular bioeconomy systems.