In this chapter, three representative thermochemical conversion techniques, i.e., gasification, fast pyrolysis, and torrefaction for lignocellulosic biomass are introduced mainly in terms of reaction, reactor, purpose, benefit, and future challenges and directions. These three conversion technologies basically use spontaneous decomposition of lignocellulosic biomass by itself. Torrefaction and fast pyrolysis, two conversion technologies at lower-to-medium temperatures, are nothing more than that. On the contrary, gasification needs gasifiers, such as oxidizing agents, steam, and carbon dioxide. In terms of target products, torrefaction produces solid fuels, fast pyrolysis produces liquid fuels and chemicals, and gasification produces gas fuels and chemicals. © 2022 Elsevier Inc. All rights reserved.