The requirement that an antitrust plaintiff show market power in rule of reason cases has an uninspiring history and unconvincing justifications. Such a requirement has never been adopted by the Supreme Court, and is currently imposed by only the Seventh and Fourth Circuits. Indeed, the requirement was never imposed very widely, despite frequent claims to the contrary. More significantly, the Seventh Circuit cases that initially established the requirement, and that continue to be cited for it, did so with misleading citations to cases from other circuits. Furthermore, the justifications that have been offered for the requirement have generally been either theoretically valid but unconnected to litigation, or empirically based but both impl...