In accordance with the goals of green chemistry, lignocellulose (or non-food) biomass is increasingly recognized as a valuable renewable energy resource. Converting biomass into liquid fuels will not only help to reduce our dependence on petroleum, but will also alleviate CO2 emissions. Designing effective, low-cost, robust, and sustainable biomass catalysts is an indispensable step for developing the next generation technologies of converting lignocellulose biomass to liquid fuels. In this chapter, we focus on current efforts to apply various catalysts in the conversion of lignocellulosic biomass polymers into liquid fuels. From the viewpoint of the fundamental chemistry, we categorize the current biomass conversion methods into three paths, and then discuss the main chemical processes and reaction mechanisms for specific biomass conversion methods, as well as the typical catalysts that are used. Since these biomass catalysts are used to perform green chemistry (i.e., producing renewable energy), we also call them green catalysts. We hope that this chapter will serve as a tutorial for green chemistry education, and inspire researchers to design more efficient, robust, low-cost, and sustainable catalytic approaches for biomass conversion.