St. Robert Bellarmine is perhaps one of the greatest controversial writers of all time. Though a humble, short and unassuming Italian Jesuit, he came to dominate the European theological scene. Bellarmine proposes 15 Marks all of which are an extension of the 4 marks which are put forth in the Nicene-Constantiplan Creed. In proposing each mark, Bellarmine examines what it entails, how it is proved in the history of the Church and how it disproves the teachings of Protestantism. This is more than an apologetic work, however, as it also brings to the fore many important distinctions of consequence in Theology.