Iggeret HaKodesh, or “The Holy Epistle,” is the fourth section of the Tanya. It comprises 32 chapters. Volume 4 of the series contains chapters 1–17. Volume 5 contains chapters 18–26. Volume 6, the final volume of the series, contains chapters 27–32, and an additional work, Kuntres Aĥaron.
Iggeret HaKodesh, or “The Holy Epistle,” is not a treatise in the usual sense of the word, with a beginning, middle, and end. Rather, it is a collection of epistles that the author of the Tanya addressed to groups of his hasidim on various occasions regarding a variety of topics. Each epistle was written as an independent unit without reference to the others. Nevertheless, it is clear that they have been thoughtfully arranged, not chronologically but thematically. Wherever possible, these thematic connections are noted in the introductions to the epistles.