The article traces the earliest history of the Slavonic Menaion for December, based on the textological research of a wide range of manuscripts of East Slav, Serbian and Bulgarian origin, dating from the 11th and until the 14th century. The multiple layers of the contents of South-Slavonic codices of the 13th - 14th century are outlined, proving, at the same time, the unconvincingness of the hypothesis for the significant influence of Old Russian originals in their formation. The study confirms the textological connection of the non-standard Russian menaia (RGADA, Synod. Typ. 98; RGADA, Synod. Typ. 130; RGADA, Synod. Typ. 131) to the Old-Bulgarian protographs. The article discloses also the unhomogeneousness of a number of offices in the East Slav menaia for December, where a more archaic layer is incorporated. The data show that the formation of the 12-volume East Slav collection is the result not of a single translation, but of a longer and gradual process of reception of the Byzantine hymnographic repertoire, starting as early as the 9th - 10th century at the literary centres of the First Bulgarian Kingdom. Therefore the Old Russian menaia reflect not the opening stage of that liturgical book in the Slavonic environment, but an older, comparatively established stage, marked by its unification, backed by approximately a century and a half of tradition.