The perception that civilization is crossing a period of Global Climatic Changes that can seriously threaten our lifestyle, along with energy security and the search for prosperity, are the main drivers that are pushing men to use more biomass as a source of energy. It will be crucial that such intent will include a large parcel of sustainability so that more renewable energy becomes available for populations. Because large amounts of energy are “hidden” in carbon polymers made by plants, notably carbohydrates, it is obvious that if technologies are developed to produce liquid fuels such as ethanol from carbohydrate polymers such as cellulose, men could significantly increase energy sustainability . This book reviews general aspects of biomass utilization for bioenergy production as well as strategies using biochemistry, molecular biology, chemistry and physics to disassemble plant cell walls. Recent discoveries of basic science under development in several laboratories in the world are reviewed by experts that have been intensively working with many aspects that will impact the development of the technology of production of cellulosic ethanol.