There seems to be consensus that the Department of Justice’s 1984 Vertical Merger Guidelines do not reflect either modern theoretical and empirical economic analysis or current agency enforcement policy. Yet widely divergent views of preferred enforcement policies have been expressed among agency enforcers and commentators. Based on our review of the relevant economic literature and our experience analyzing vertical mergers, we recommend that the enforcement agencies adopt five principles: (i) The agencies should consider and investigate the full range of potential anticompetitive harms when evaluating vertical mergers; (ii) The agencies should decline to presume that vertical mergers benefit competition on balance in the oligopoly markets ...