Biomass is the most important renewable energy option at present and is expected to maintain that position during the first half of this century. Forest and wood process residues can be converted into useful bioenergy. The structural components of wood are cellulose, hemicelluloses, and lignin. Fuelwoods are composed of biopolymers that consist of various types of cells and the cell walls are built of cellulose, hemicelluloses, and lignin. The fuel properties of wood can be summarized by elemental and proximate analyses and determination of heating value. Cellulose has a smaller heating value than lignin because of its higher degree of oxidation. Elemental H and C contents of fuel and lower degrees of oxidation tend to raise the heating value of the biomass. Woods are either hardwoods or softwoods. Softwood species generally have higher carbon content and higher heating values than hardwood species because of the presence of more lignin and resinous materials in softwood species. Extractives raised the higher heating values of the wood fuels. Heating value of a wood fuel decreases with increasing of moisture content of the wood.