Greg has worked in the Antitrust Division of the U.S. Department of Justice since 1977. He earned several degrees including a Ph.D. in economics from the University of Wisconsin. He was the principal author of the 1982 and 1984 Merger Guidelines, as well as four other sets of enforcement guidelines. He assisted in the preparation of over forty amicus briefs filed with the Supreme Court and the courts of appeals, and worked on all appeals of the DOJ civil antitrust cases since 1985. He has published extensively on antitrust policy, particularly on market delineation and the quantitative assessment of unilateral merger effects.