Frank Knight's theory of monopoly price has received relatively little attention in the literature on Risk, Uncertainty and Profit. We argue that Knight accepted and refined the monopoly price theory of Carl Menger and his followers. Knight highlights the difference between monopoly as an inevitable outcome of departures from perfect competition, and monopoly as a contingent or ‘culture-history fact’. In the latter case, coercive institutional barriers to potential competition shape the choice set of consumers and producers, and provide a crucial method for identifying monopoly gains. There are three benefits to this account of Knight's contributions: it rehabilitates the focus on the institutional determinants of monopoly price, as opposed to the mainstream emphasis on market frictions and imperfections; it opens the way for a Mengerian monopoly price theory that seriously engages the study of institutions; and it adds new evidence and nuance to ongoing debates about Knight's place in economics.