From the 4th/10th century onwards, large numbers of letters (arab. rasā'il, the common distinction is between dīwānīyāt, "chancery letters", and ikhwānīyāt, "letters between friends") have survived to our time, both in letter collections and other works (e.g., literary anthologies). The survival of so many letters from the writers of the Buyid period stands in constrast to the earlier Islamic centuries from which relatively few letters have survived, although it had been customary among high-ranking scribes to collect and publish their letters from late Umayyad times onwards. This study examines how letters were treated: (a) in early works of literary criticism; (b) in the so-called adab al-kātib literature (scribe manuals); and (c) in literary anthologies (florilegia). In all three areas, it is possible to trace a growing "literarization" that resulted in the emergence of a so-called ornate prose style that came to dominate Arabic epistolography in the 4th/10th century.