For decades, the nation has benefited from relatively inexpensive energy, in the process growing heavily reliant on conventional fossil fuels -- oil, natural gas, and coal. However, in the current wake of higher energy costs and environmental concerns about fossil fuel emissions, renewed attention is turning to the development of advanced energy technologies as alternatives. In the United States, the Department of Energy (DOE) has long conducted research, development, and demonstration (R&D) on advanced renewable, fossil, and nuclear energy technologies. DOE's Office of Science has also funded basic energy-related research. This book presents important information of developments in this essential field.