Although scholarship has treated, on the one hand, some aspects of Jacobus Arminius’s theology, and on the other hand, the doctrine of assurance in the Reformed theologians of early Protestant orthodoxy, nevertheless proper attention has not yet been given to the intersection of these topics: Arminius’s doctrine of assurance. With special attention to previously neglected primary sources, this book offers stimulating insights into the academic context of Arminius, and, along with a comparative analysis of his colleagues at Leiden University, explores new horizons in his doctrines of salvation and assurance. Arminius’s search for true assurance of salvation emerges as a decisive factor in his famous dissent from Reformed theology.