Energy engineers, technology managers, and political leaders all need a solid, holistic understanding of where the world finds its energy - the limits of that energy - and what we will need to do in the future if we are to have a cleaner and environmentally sustainable world, all without sacrificing our modern technological-based civilization. This book will shed some much needed light on that conundrum. It provides a broad overview of our current energy sources, their uses and limitations and political and economic constraints. It clarifies the urgency behind the sweeping changes in the world's energy needs and available supplies. It offers a rational paradigm for how we can go about selecting the optimal mix of fossil, renewable and sustainable energy sources and how we can then aggressively move toward those more sustainable sources. Drawing from a combined 40 years of teaching about energy and its applications, the authors offer a broad, balanced analysis of our current energy circumstances and how we can intelligently transition from our reliance on fossil fuels to more sustainable and renewable energy sources - solar, wind, nuclear, and bio-mass. With their grounding in the traditional petroleum industries, the authors embed their arguments for cleaner and more sustainable energy sources in the hard realities of energy economics. Those hard realities include the enormous 'energy density' advantage that oil and gas currently provide over other alternative energies and how that must always enter into any rationale economic plan for future energy growth.