The demand for energy is increasing rapidly every year in every country, including Nepal. In order to meet the growing demand for energy, different kinds of alternative energy sources can be used, of which biogas is worth mentioning. Biogas, which is considered an ideal energy converter, burns much more efficiently, and the residue, sludge, is a better fertiliser than the raw dung, providing the output over twice as much heat and nearly three times as much useful fertiliser as would have been obtained from the original dung. The manure produced from biogas plants can be used as a better organic fertiliser by 20 to 30 percent than other compost fertilisers. In addition, the residue, sludge, produced from these plants kills the weeds and helps every crop thrive luxuriantly. Human waste and some vegetation waste can also be used in biogas plants. Since proper treatment eliminates some pest disease carrying organisms, it improves the sanitation of a country. The use of biogas not only reduces cooking time but also saves the consumption of kerosene, which has to be imported from other countries using scarce foreign exchange. To operate pumps and other machines, the clean smokeless gas emitted from biogas plants can be used. Apart from reducing deforestation, the use of biogas helps maintain an ecological balance indirectly and stimulates the stable feeding of livestock. By using biogas plants, foreign currency which otherwise would be spent in importing different kinds of fuel, can be saved considerably and utilised in productive sectors. Since forests are shrinking every year in the world, there are not encouraging signs of obtaining the necessary quantity of firewood in the future. Since switching to fuels such as gas or kerosene is not possible for all people, agricultural residues can serve as the alternative to firewood for millions of people living in the developing and the least developed countries. Although crop residues burn quickly, making cooking a more time consuming and tedious activity, woody crop residues can be used as the best cooking fuel. Cocoa nutshells, jute sticks and millet stalks burn well and are gaining popularity in most countries, especially in the least developed ones. Furthermore, solar and wind energy can meet the growing energy needs of the people. Though they are very expensive to tap, they are renewable and everlasting. Therefore, it is expedient to pay special attention to harnessing such energy as the cost of producing power from solar and wind has come down considerably over the years.