Professor Manaster studied in Peru on a Fulbright Fellowship; served as a law clerk for Judge Bernard M. Decker of the U.S. District Court in Chicago; and was in private practice in Chicago. In 1970, he became an assistant attorney general of Illinois, heading the Chicago office of the attorney general's Environmental Control Division. He also has taught at the University of Texas and the University of California's Hastings College of the Law. He has held the position of visiting scholar at Harvard Law School and Stanford Law School.