This article will examine Bellarmine’s first anti–conciliarist work, found in the Disputationes de controversiis Christianae fidei adversus huius temporis haereticos, emphasizing his theological treatment of the pope’s authority relative to the authority of a council and his repudiation of conciliarism. Bellarmine sees the conciliarists as attacking the divinely instituted Petrine structure of the Church. He does not advocate for an absolute papal monarchy in which there are no ‘constitutional’ limitations on the papacy. For Bellarmine, Christ and his Word, as found in Sacred Scripture and Apostolic Tradition, have supreme authority in the Church: one which the magisterium, whether papal or conciliar, must accept in humility and pass on unsullied. Only Christ has a true fullness of power; the pope has a fullness only relative to that of the bishops. Nevertheless, Christ immediately instituted the pope as the supreme head of the Church on earth, and as such, the pope has supreme ecclesiastical power over the whole Church on earth. Lastly, the article examines Bellarmine’s position on papal heresy.