The NASA Astrobiology Institute (NAI) was established as a means to advance the field of astrobiology by providing a multidisciplinary, multi-institution, science-directed program, executed by universities, research institutes, and NASA and other government laboratories. The scientific community and NASA defined the science content at several workshops as summarized in the NASA Astrobiology Roadmap. Teams were chosen nationwide, following the recommendations of external review groups, and the research program began in 1998. There are now 16 national Teams and five international affiliated and associated astrobiology institutions. The NAI has attracted an outstanding group of scientific groups and individuals. The Institute facilitates the involvement of the scientists in its scientific and management vision. Its goal is to support basic research and allow the scientists the freedom to select their projects and alter them as indicated by new research. Additional missions include the education of the public, the involvement of students who will be the astrobiologists of future generations, and the development of a culture of collaboration in NAI, a "virtual institute," spread across many sites nationally and internationally.