The subject of the present research is an anonymous letter writing manual, written in the 12th – 13th c. (further, Ch40). The treatise includes 40 letter models relating to 40 types of letters. Names of types go back to Pseudo-Libanios’ treatise Characteres epistolici (5th c.). It is very likely that the Ch40 was used as a school textbook during the course of rhetoric, and its model letters functioned, in particular, as exercises on the theory of rhetorical argumentation. In this article, we are trying to prove that the Ch40 is not only a collection of rhetorical exercises, but also a practical guide to epistolary art. For this purpose we consider model letters in the context of the epistolary practice of the 9th – 15th cc. The examples of the “friendly”, “wishing”, “replying” and “mixed” letter types are analysed. It is demonstrated that these letters contain not only the etiquette motives and ideas typical for epistolography, but also a number of phrases and clichés, which are used in many letters of the middle and late Byzantine period. It is pointed out that Ch40 pays special attention to letters of request, in which the author addresses a high-ranking addressee and asks for material assistance or intercession. This variety is represented by 4 letters formally belonging to 4 different types. This group includes the “mixed” letter, the most extensive in the collection. The ability to write a petition correctly and gracefully was in great demand, and the attention paid to this type of letter in Ch40 is a clear evidence of its practical orientation. As a practical guide to ars epistolandi, the Ch40 differs from other manuals of this kind, which were used exclusively as school textbooks.