This article introduces the unedited Homily on repentance composed by Kallistos I, patriarch of Constantinople in late Byzantium. It first offers a biographical portrait of the author, discussing the historical context of his activity, and continues with a brief presentation of his homiletical corpus and the editorial work it attracted, focusing on the manuscript tradition, date, and content of Patriarh Calist’s Homily on repentance. The second part of the article offers the text of the Homily, transcribed on the basis of the fourteenth-century manuscript Hilandar 8 (Lambros 229), as well as its translation into Romanian. The article is equipped with a plate from the Athonite codex.