As a clean, renewable energy source, bioenergy is among the most alluring substitutes for fossil fuels. Although lignocellulose’s diverse and resistant structure is a drawback, it offers enormous promise for bioenergy technology. Bioconversion of waste biomass into bioenergy (bioethanol, biogas, biohydrogen, etc.) has recently benefited from the advent of biochemical pretreatment techniques that make the process more efficient than before. Nonetheless, various pre-treatment methods, as a combination, have been reported to be effective with better delignification extent as compared to a single pre-treatment method used in isolation. Chemical pre-treatments are the ones more researched because of their efficiency and minimum treatment time. In this chapter, the developments of conventional and novel technologies for the pretreatment of lignocellulose were systematically reviewed, and advances in bioenergy from pretreated lignocellulose were presented with emphasis on major challenges. The information provided in this chapter may be used to help advance lignocellulosic bioenergy production with the ultimate goals of minimizing the worldwide energy crisis and climate change resulting from fossil fuel burning. This chapter provides a comprehensive review of chemical and biological pre-treatment technologies and a discussion of their applicability and successful results to understand their influence on bioenergy industries.