The use of biomass as a source of energy varies in different countries and depends in part on the country’s level of development. In many developing countries, biomass provides most of the basic energy needs, mostly as fuelwood, animal wastes or crop residues while in developed countries only a fraction of their energy requirement comes from agriculture and agro-industrial wastes. In the United States for example, biomass conversion amounts to about 3.25% of the energy supply (EIA, 2002 and Haq, 2002) while in Bhutan, the share of biomass energy in total energy use accounts for about 87% (Victor, and Victor, 2002). Biomass resources could play a significant role in meeting the future energy requirements. However, the approach in their utilization should be carefully analyzed in view of diverse cultural, socio-economic and technological factors in a given locality. Agricultural and agro-industrial wastes can provide an inexpensive source of energy and effective low sulphur fuel. It could be processed into other fuels thereby reducing environmental hazards (e.g. biomass from sewage). Also, there is relative ease with which it could be gathered and generated. However, the conversion of light energy into biomass by plants is relatively of small percentage and there is relatively low concentration of biomass per unit area of land and water. The additional land for biomass production is getting scarce, and the high moisture content of fresh biomass makes collection and transport expensive. Thus, biomass energy conversion could be relatively inefficient. Moreover, extensive utilization of these resources may compete with the demand for these as food. These are some of the issues concerning the extensive utilization of biomass resources. In view of the depleting forest and agricultural resources for energy use, attention should be focused on new and emerging technologies for their efficient conversion. There are a number of sources of energy for both rural or agricultural and urban or industrial residues. There is a need to diversify the traditional resources for energy to meet the demands. These include, among others: (1) planting high energy value crops, fast growing trees, sugar and starchy crops, aquatic plants, oil and hydrocarbon crops, and (2) getting energy from municipal sewage and solid wastes. Some common properties of biomass resources will be reviewed to gain perspective of biomass as a source of energy compared with traditional fossil fuel sources. The primary advantage in the use of biomass as an energy resource is that it is a renewable feedstock and does not contribute to global warming.