John Fisher's career as a polemical theologian did not begin until 1519, his fiftieth year, and, since his previous publications had all been of a devotional or pastoral nature, there was nothing in his background – except perhaps his Yorkshire birth – to suggest that he would become such a tenacious controversialist. This clearly sets him apart from such humanist or scholastic contemporaries as Cajetan, Clichtove, Eck and More, whose argumentative dispositions became apparent far earlier in their careers. Yet, despite his lack of experience, his works against Lefevre d'Etaples, Luther and Oecolampadius earned him a reputation as a theologian of considerable weight. Indeed, Lord Acton was to write, cOf all the works written against Luther in the beginning of the Reformation, his [Fisher's] were the most important.’ Although it might be argued that this was a dubious accolade, Acton's judgement is confirmed by the esteem in which Fisher and his work were held even before his martyrdom, by the success of his books, and by the use made of his work in later Catholic polemics and at the Council of Trent. But, before considering the motives which led Fisher to engage in theological controversy, and the qualities which made his works, at least in Catholic circles, among the most influential of their time, it is worth setting the scene by sketching the course of his polemical career. This can be conveniently divided into two phases, separated by the watershed of the condemnation of Luther in 1520.

In the earlier period, Fisher was embroiled in an often acrimonious debate over the identity of Mary Magdalene.