The Libri Epistolarum Sancti Patricii Episcopi, the Book of Letters of St. Patrick the Bishop, is the name Ludwig Bieler gave to St Patrick's opuscula, including the Confessio and the Epistola ad milites Coroticus. Bieler constructed his edition from eight surviving manuscripts of various date but dates the exemplar to the fifth or sixth century, though the earliest surviving version was copied c. 800 in what is now known as Book of Armagh. This codex, including the Psalter, Gospels, the entire New Testament, the Liber Angeli, and the Lives of St Patrick and St Martin, as well as Patrick's writings, was written to be the personal devotional book of Toarbach, coarb of Patrick. In the manuscript, the Patrician texts begin: Incipiunt libri sancti Patricii episcopi (‘Here begins the book of St Patrick the bishop’). This section of the Book of Armagh is the work of two scribes, including the Armagh scriptorium's master scribe, Ferdomnach, and they represent incomplete versions of the Epistola and Confessio.

While the earliest manuscripts do not appear to have survived, the eight surviving manuscripts are believed to accurately represent the original exemplar, as the copies were not influenced by the romantic style of the early Bardic tradition in Ireland. Concerning this matter, Ludwig Bieler argues,

Bieler's thesis is widely accepted and has helped to set aside concerns that the manuscripts, copied over several centuries, are tainted by the rhetorical, stylistic, grammatical, and thematic tendencies of redactor context. The version of the Confessio in Book of Armagh, however, does leave out an important section on Patrick's childhood sin. However, considering the propagandistic ends to which the early manuscripts were put by the hagiographers Muirchú and Tírechán in order to claim superiority for the ecclesiastic community at Armagh, that the Libri Epistolarum remained mostly unchanged is remarkable.