This article reviews the production processes and characterization of biogas as an alternative energy source. Biogas, the gas generated from organic digestion under anaerobic conditions by mixed population of microorganisms, is an alternative energy source, which has been commenced to be utilized both in rural and industrial areas at least since 1958. Biogas technology offers a very attractive route to utilize certain categories of biomass for meeting partial energy needs. Unlike other forms of renewable energy, biogas neither has any geographical limitations and required technology for producing energy and it is neither complex or monopolistic.