This book is an overview of the Solar Energy Technologies Program in the U.S. The U.S. Department of Energy is committed to "discovering the solutions to power and secure America's future, which include clean energy technologies that not only enhance energy independence but also can reduce greenhouse gas emissions and criteria air pollutants. The Department's robust activities to support the development of solar energy technologies include applied research in support of the Solar America Initiative in the Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Program as well as important exploratory research in the Office of Science.