Astrobiology is a scientific discipline devoted to the study of life in the universe - its origin, evolution, distribution, and future. In 1997, NASA established an Astrobiology program (the NASA Astrobiology Institute - NAI) as a result of a series of new results from solar system exploration and astronomical research in the mid-1990s together with advances in the biological sciences. To help evaluate the NAI, NASA asked the NRC to review progress made by the Institute in developing the field of astrobiology. This book presents an evaluation of NAI\'s success in meeting its goals for fostering interdisciplinary research, training future astrobiology researchers, providing scientific and technical leadership, exploring new research approaches with information technology, and supporting outreach to K-12 education programs.