AT&T/Time Warner is the U.S. Department of Justice’s first vertical merger challenge in decades. The merging parties hired us initially to provide economic analyses of the antitrust issues raised by the merger and ultimately to assist with and testify in the litigation. There are three keys lessons that we draw from the outcome of the litigation for future antitrust practice. First, history matters, particularly the outcomes of similar integrations or mergers, both in predicting price effects and in testing merger simulation models proposed by economic experts. Second, one should be careful of simulation models of vertical transactions as they can be complicated and fragile. Third, the fact that the courts credited cost-saving efficiencies as credible, cognizable and relevant to the analysis of net harm is likely to be important for the analysis of future mergers, as the role of efficiencies in merger litigation remains an open question.