This is an important and original biography of John Colet, the leading humanist theologian in early Tudor England and the founder of St Paul’s School in London. Taken at face value, the facts of John Colet’s life, spanning the late 15th and early 16th centuries, appear to portray a successful, humanist clerical reformer, active in London on the eve of the English Reformation. In fact, as a cleric, John Colet was neither successful nor a reformer, nor were the reforms he attempted particularly welcome. His greatest achievement, and lasting legacy, was the foundation of his school. Thus, in the sphere of Christian humanist education, Colet was a success. However, in all his dealings, Colet considered the spiritual life to be of paramount importance and his ultimate aim was the deification of sinful humanity, not just for a few exceptional individuals, but for the entire Church. In this respect, Colet’s ecclesiastical vision did not effect any significant change in the early sixteenth-century Church, although it nevertheless pointed to the possibility of a more spiritual, unified and holy Church. Colet was a passionate and pious man who does not fall easily into any historical, intellectual or ecclesiastical category. Ultimately, he escapes identification with any other set of contemporaneous idealists because his vision was his own. This study offers a timely re-assessment of the life of a complex religious figure of pre-Reformation England.