Around the 1860s, technological advancements in transport, communication and warehousing, contributed to the emergence of world markets for many staple commodities (e.g. cotton, wheat). At the same time, the economic needs of the companies involved in this commercial revolution stimulated the growth of markets for stocks and shares. The growing complexity of global markets created propitious conditions for the emergence of a class of professional speculators capable of processing a large body of information and of relieving producers and traders of the risks deriving from price fluctuations. Initially, the frenzy that accompanied this process seemed to confirm traditional views, which identified speculation with gambling. With time, however, a new literature emerged, free from moral considerations. Our analysis brings to light how contributors to this new literature, confronted with the novelty of globalized asset markets, made the case for speculation against conventional wisdom. In so doing, they were not blind to the downside effects of speculation, as a possible source of resource misallocation. Nevertheless, they chose to emphasize its constructive side, basing their arguments on the case of commodity markets, where the idea of a long-run equilibrium price to be attained by speculation appeared plausible. They employed the same arguments in the case of the Stock Exchange, downplaying differences between the two markets although they were well aware of them. Thus economists played a crucial role in convincing policy makers of the beneficial effects of the new speculative instruments, against the combined hostility of a large part of public opinion. Many have already explored the rise of this literature. The goal of this paper is to expand this line of research, focusing on theories formulated in the Anglo-Saxon tradition between the second part of XIX century and 1929. To this end, we combine evidence drawn from manuals aimed at practitioners , chapters in books on Political Economy  and scientific literature on speculation either in the form of treatises  or articles.