Today, the energy sources used to create electricity differ in many ways, including in their environmental impacts. In the United States, electricity is most often generated using fossil or nuclear fuels -- forms of power generation that can have detrimental effects on human health and the environment through air emissions and other problems. Despite advances in pollution controls over the last 30 years, this conventional power generation is still the nation's single largest source of industrial air pollution and is a major contributor to greenhouse gas emissions. Electricity markets now offer cleaner ways of producing power, however, and give many consumers the ability to choose how their power is generated. One of these choices is power from renewable sources, or "green power". This book is a guide to purchasing green power and a summary of federal renewable energy and energy efficiency programs.