In 1539 Cardinal Jacopo Sadoleto, Bishop of Carpentras, France, sent a letter to the magistrates and citizens of Geneva asking them to return to the Catholic faith. A few months later, John Calvin replied to Sadoleto, defending the Protestant reforms. Both letters are lucid and eloquent statements of their espective positions. Their dialog is polemical, but their tone is elevated and their arguments substantial. The letters of Calvin and Sadoleto comprise one of the most interesting exchanges of Catholic-Protestant views of the Reformation era. Together, they form an excellent introduction to the great religious controversy of the sixteenth century.