Human survival depends on a continuing energy supply, but the need for ever-increasing amounts of energy poses a dilemma: How can we provide the benefits of energy to the population of the globe without damaging the environment, negatively affecting social stability, or threatening the well-being of future generations? The solution will lie in finding sustainable energy sources and more efficient means of converting and utilizing energy. This textbook is designed for advanced undergraduate and graduate students as well as others who have an interest in exploring energy resource options and technologies with a view toward achieving sustainability. It clearly presents the trade-offs and uncertainties inherent in evaluating and choosing different energy options and provides a framework for assessing policy solutions.