During the 1980s, the biomass power industry became the second largest of all renewable energy industries in the United States of America. In 1991, the Biomass Power Program was formed to meet the research and development needs of this rapidly growing industry. Biomass is biological material derived from living, or recently living organisms. It most often refers to plants or plant-based materials which are specifically called lignocellulosic biomass. As an energy source, biomass can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuel. Conversion of biomass to biofuel can be achieved by different methods which are broadly classified into: thermal, chemical, and biochemical methods.