The paper deals with the history of the antitrust offense of predatory pricing in US antitrust law. Despite being considered so serious a violation to deserve a per se condemnation, predatory behavior has never been easy to identify in real markets because pricing at a very low level is normally welfare-enhancing. For most of the 20th-century the violation has been severely enforced by US courts, though on the basis of a legal argument devoid of solid foundations in theoretical economics. The paper examines the critiques against this argument made by Chicago scholars, the literature stemming from these critiques and the motivations behind the U-turn in enforcement triggered by the influential contribution by Areeda & Turner (1975). This story may tell a useful lesson about the different practices of economists, legal scholars and judges with respect to the treatment of antitrust violations.