Isabella d'Este (marchesa of Mantua, 1490–1539) desired personal authority in the political, cultural, and social spheres, while also seeking dynastic advancement. Her extensive correspondence, now in the Mantuan State Archive, was a key instrument of aggrandisement. It reveals Isabella's image management, her manipulation of the epistolary form, and the power-sharing dynamic with her husband Francesco Gonzaga. This article examines letters in which Isabella used masked simulatory or dissimulatory communication in pursuit of her aims. These epistolary masking techniques range from ciphers, with undisguised concealment, to entire fake letters. The use of letters as works of art and artifice is also seen in Isabella's expert forging of a letter from her absent husband in order to trick a Borgia spy, an example demonstrating teamwork of husband and wife. Such masking strategies provide an excellent illustration of self-presentation and power sharing in action.