This chapter introduces the basic theory and technologies of biochar production, biochar activation and upgrading, and biochar application as a promising catalyst. The routes of biochar production including conventional pyrolysis, gasification, microwave assisted pyrolysis and hydrothermal carbonization are described in detail. The yield and properties of biochar, such as high heating value, pH value and BET surface area and pore structure, and also the graphitization degree, are significantly affected by operating conditions, temperature, heating rate, solid residence time, particle size, etc. To enhance the pore volume, control the pore diameter, and improve the surface area of primary biochar, physical activation, chemical activation, and the physicochemical activation are the main technologies. After activation, biochar has a relatively high surface area and pore volume possessing a multi-level porous structure with both micropores and mesopores. And the functional groups on the surface of biochar facilitate its surface chemistry modification. Because of all of these properties, biochar has a great potential for application as a catalyst and catalyst support. The catalyst applications summarized in this chapter include the direct application of biochar as a catalyst for biomass thermoconversion and tar removal, heterogeneous catalyst support for hydrocarbons production, solid acid catalyst for biodiesel production, electrochemical catalyst and photocatalyst.