The letters exchanged between Byzantine emperor Constantine VII Porphyrogenitus (913-959) and his close friend Theodore, Bishop of Cyzicus, are of the utmost importance, representing the only preserved example of authentic writings from the emperor. Other than the fact that the correspondence offers details concerning the relationship between Theodore and Porphyrogenitus and their personal lives, it also provides a good foundation for the study of Porphyrogenitus’ style of writing, which is very useful considering that the authorship of the emperor’s literary inheritance is still the object of scholarly discussion. The corpus of this study is made up of ten letters written by Theodore and addressed to Constantine (whose letters of reply have not been preserved) from the Vindobonensis Collection and correspondence between Theodore and Porphyrogenitus from the Athos Collection (ten of Theodore’s and eight of Constantine’s letters). Epistolary topoi found in the letters will be analyzed and divided into two groups: contemplative and linguistic. The aim is primarily to present the features of Porphyrogenitus’ letter-writing style, but also that of his correspondent, with special reference to the extent to which rhetorical recommendations were followed when composing letters.