Law clerk to Justice Potter Stewart, Supreme Court of the United States Court, Washington, 1960-1962. Associate firm Sidley & Austin, Chicago, 1962-1964. Assistant professor University Michigan Law School, Ann Arbor, 1964-1967, associate professor, 1967-1969, professor, 1969—2008, Henry M. Butzel Professor Law, professor emeritus, since 2008.
On leave as deputy assistant attorney general Office Legal Counsel, Department Justice, Washington, 1969-1971. Assistant attorney general antitrust division United States Department Justice, 1972-1976. John M. Olin Visiting Professor of Business, Economics, and Law Harvard Law School, Cambridge, Massachusetts, 2002.