In recent years, the applications of lignocellulosic biomass (LCB) have substantially increased due to its versatility in different areas of study and interest. Therefore, it is evident that the delignification pretreatment of LCB is fundamental to assure the viability and commercial quality of the final product for different industrial uses. The efficiency of delignification, the obtainment of the desired products, and the required quality depend mainly on the type of pretreatment and the method used. This paper presents a state-of-the-art overview of physical, chemical, organic, biological, hybrid (combination of two or more pretreatments), and other novel pretreatments for the delignification of different lignocellulosic biomass. Additionally, the conditions necessary for the application of the pretreatments, the effect of the variables involved, and the advantages and disadvantages of each method are discussed. Finally, advances in the development of sustainable methods are discussed.