This chapter focuses on thermochemical conversions of biomass. Conversion techniques can be mainly categorized as combustion, gasification, and pyrolysis. Combustion of biomass directly releases the chemical energy stored in biomass in the form of heat through complete oxidization and is the most direct way of converting biomass to energy. Gasification and pyrolysis, however, offer efficient ways to produce gaseous, liquid, or solid products that are capable of being energy carriers or intermediate platforms for valuable chemicals. The successful long-term sustainability of biomass-to-liquid fuels technology depends on the effective conversion of biomass into products that are compatible with existing transportation and refinery infrastructure. The composition and quality of syngas produced are directly related to biomass properties, gasifier design, and operating conditions and downstream syngas cleaning and conditioning. Pelletized or otherwise densified biomass exhibits better fuel operability than raw biomass. Torrefied biomass pellets are commercially attractive commodities that have potential to substitute regular pellets for bioenergy production.