Thomas Aquinas did not write a treatise on risk in economics or even on risk in general. He was writing before the theorisation of risk that gradually emerged from the calculation of probabilities in the modern era to the present day. Despite this, the study of Aquinas’s treatment of risk has proved fruitful for three reasons: the importance he attaches to economic activity, the period in which he was writing, and the call for a long-term approach to history of economic thought. In addition, Aquinas is often studied for his contribution to economic ethics, but he deserves to be studied from the angle of economic analysis, for his contribution to the understanding of activities and mechanisms.