Electricity in the United States has traditionally been generated largely from coal, natural gas, nuclear, and hydropower energy sources. More recently, various federal and state policies, tax incentives, and research and development efforts have supported the use of renewable energy sources such as wind, solar, and geothermal. In addition, consumption of electricity has been affected by federal efforts to improve energy efficiency, changes in the economy, and other factors. This book examines what is known about how electricity generation and consumption have changed since 2001, and the implications of these changes on efforts to maintain reliability, and on electricity prices.