Stephen L. Brock is a priest of the Prelature of Opus Dei. He holds a BA in Philosophy from the University of Chicago and a PhD in Medieval Studies from the University of Toronto. Since 1990 he has taught medieval philosophy at the Pontifical University of the Holy Cross in Rome. He has been a visiting professor in the Philosophy Department of the University of Chicago since 2017. His research has been mainly on the thought of Thomas Aquinas, in the areas of ethics, action theory, and metaphysics, with occasional ventures into theology. His most recent book is The Philosophy of Saint Thomas Aquinas: a Sketch (Wipf & Stock, 2015), and he has a book forthcoming on Aquinas’s metaphysics of natural law.