No other theological text polarized the early modern Catholic world as much as Cornelius Jansen's Augustinus. In it the erudite bishop not only reconstructed St. Augustine's teaching on grace and free will, but also threw down the gauntlet to the Council of Trent and the Society of Jesus. For Jansen the latter had marginalized the Church Father's doctrine on divine predestination by overemphasizing human free will. Published after his death in 1640, Jansen's work drew a large crowd of followers and inspired an Augustinian reform movement. Its papal condemnation unintentionally spread this theology, but stifled an impassionate, academic engagement with the Augustinus. This first-ever translation of some of its central chapters enables historians, philosophers and theologians to finally engage with the founding text of Jansenism.