This extended study of Thomistic concepts in the work of Franciscus Junius (1545–1602) is the first English monograph on Junius’s theology in more than 40 years, and the first analysis of his use of Thomistic moral concepts. On a broad level, this project investigates the reception of Thomistic ideas in the early modern Reformed tradition. On a narrow level, this study contributes to an examination of Junius’s moral theology itself.