What do we want from sustainable energy? What is possible to achieve and when? Energy professionals and political leaders need a solid, holistic understanding of where the world finds its energy—the limits of that energy—and what must change in the future if we are to have a more environmentally sustainable world, all without sacrificing our modern technologically-based civilization. This book sheds some much needed light on that conundrum. It • provides a broad overview of our current energy resources and their limitations; • includes considerations of political and economic constraints, especially the enormous “energy density” advantage that oil and gas currently provide over alternative energies and how that must always enter into any rational plan for future energy supplies; • investigates societal uses of energy and potential for supplying projected future needs for both the Developed and Developing Worlds; • discusses energy production methods that contribute to sustainability challenges; • clarifies the urgency behind the sweeping changes in the world’s energy needs and available supplies; • discusses the transition viability of nuclear, biomass, solar, wind, hydro, wave, tidal, and geothermal energy sources; and • offers rational evaluations of time frames and energy development directions to accomplish sustainable mixes of fossil and renewable energy sources, with an emphasis on contexts, including energy needs in poor countries.