Sagan holds a B.A. in Government from Oberlin College (1977) and a Ph.D. from Harvard University (1983). He spent the junior year of his undergraduate degree at the University of Aberdeen in Scotland. Before joining the Stanford faculty in 1987, Sagan was a lecturer in the Department of Government at Harvard University and served as special assistant to the director of the Organization of the Joint Chiefs of Staff in the Pentagon. He has served as a consultant to the office of the Secretary of Defense and at the Sandia National Laboratories and the Los Alamos National Laboratory.