The energy hold on in biological resources may be born-again into helpful energy services like heat, power, and transportation fuels. This text presents definitions like energy crop, by-product and waste, and classifies biological materials in line with their composition in four groups: lignocellulosic biomass,sugar and starches,oil biomass,and high-moisture biomass. Common primary and secondary conversion technologies for those teams also are in short mentioned. Biomass is seen because the renewable energy supply with largest potential,however environmental and socio-economic impacts of bioenergy systems ought to be accurately evaluated so as to ensure property systems.