Thermochemical processing of biomass uses heat and catalysts to transform plant polymers into fuels, chemicals, or electric power. Thermochemical conversion can be categorized as combustion, gasification, pyrolysis, and solvent liquefaction. The key operating parameters governing these routes are degree of oxidation, temperature, heating rate, and residence time. Among the thermochemical technologies, combustion is the most widely deployed in commercial practice. The commercialization of second‐generation biofuels is widely limited by their high cost of production, which can be as much as two to three times higher than for fossil fuels. Biofuels produced from sustainably grown biomass have several environmental benefits compared to petroleum‐derived gasoline and diesel. Among the most important of these is net reductions in life‐cycle GHG emissions, which arise from the fact that the carbon in biofuels is taken up from the atmosphere through photosynthesis of growing biomass. This introduction also presents an overview of the key concepts covered in this book.