Lignocellulosic biomass is a naturally occurring carbon source that is produced in large quantities worldwide from a variety of food processing, agro, and food-related industries. However, the tightly snarled structural and physical characteristics make it difficult to convert lignocellulose into bio-based products in the biorefinery process without pretreatment. However, lignocellulosic biomass can be successfully and efficiently converted into biofuels like bioethanol, biodiesel, and biogas, as well as value-added products like organic acids, biopolymers, biochar, enzymes, and so on. This process isolates the cellulose and hemicellulose from the complex polymer matrix’s lignin, reduces the matrix’s size, and raises the cellulose and hemicellulose’s surface area, making them more accessible to enzymes and microorganisms for fermentation and hydrolysis. The pretreatment process includes physical, chemical, physicochemical, or biological. Mechanical milling, ultrasound, and microwave radiation as physical; acid/alkaline hydrolysis, ionic liquids, and ozonolysis as chemical; ammonia fiber explosion, CO2 explosion, steam explosion, and liquid hot water treatment as physicochemical methods were established. The use of certain species of bacteria, fungi, and yeast in biological methods of pretreatment is yet to be established on a large scale. This chapter comprehensively reviews the novel technologies and chemicals that were applied in the various pretreatments. In addition, the mechanisms, advantages, and disadvantages of the updated pretreatments are discussed to provide a reference for developing new pretreatment methods.