This study is in its broadest sense an inquiry into the intellectual origins of the Reformed branch of Protestantism generally, but inaccurately, designated Calvinism. More specifically, it concerns one of the early theologians who gave formative shape to Reformed theology, Peter Martyr Vermigli (1499-1562), and focuses on his adoption of the soteriological doctrine of gemina praedestinatio, double predestination: divine election and divine reprobation. One of the most erudite men of his age, Vermigli was also one of the most remarkable, for his religious career spanned the ecclesiastical horizon from prominence as a Roman Catholic theologian to one of the formative theologians of sixteenth century Reformed Protestantism. No other theologian of the early sixteenth century was so distinguished in both camps. James argues that Vermigli derived the doctrine of gemina praedestinatio from the writings of Gregory of Rimini and that it was fully formed before he allied himself with the Protestant cause, thus illustrating an important aspect of soteriological continuity between late medieval and reformation thought.