This article examines the questions occupying the newly formed transatlantic working group of leading antitrust enforcers (the EC, the FTC, DoJ, Canadian Competition Bureau and CMA) as it embarks on a mission of determining whether new principles by which to assess a pharmaceutical merger’s effects on innovation are warranted. The article examines sometimes-conflicting cases and merger analyses from both sides of the Atlantic and explores practical issues relating to evidence, counterfactual analysis and remedies, which it invites the working group to consider.