The purpose of this essay is to shed light on how female correspondence functioned as a vehicle for religious subversion in sixteenth-century Italy. This theme will be explored by way of the letters-both written and received--of Giulia Gonzaga (1513-1556), famous in her generation for her beauty and piety, as well as for her religiously heterodox friends, almost all of whom were the focus of investigation by the Roman Inquisition. The essay explores how, for two decades between the mid-1540s and 1560s, private letters were a valuable mode of communication for Gonzaga and her dispersed religious associates, especially in the most dangerous decade, the 1550s. The basis of this article is Gonzaga's correspondence. Having been widowed at a young age, and following a bitter inheritance dispute, she lived most of her adult life in a Neapolitan convent, from where she conducted her business affairs largely by letter. As a member ofthe famous Lombard Gonzaga dynasty (her second cousins were the Dukes of Mantua; her immediate family held the neighboring territory of Sabbioneta), she wrote prolifically to her northern Italian relations and their agents concerning family and state affairs, with over 300 of these letters extant.