For the next 15 years, until he died, Jerome produced a number of commentaries on Scripture, often explaining his translation choices in using the original Hebrew rather than suspect translations.
His patristic commentaries align closely with Jewish tradition, and he indulges in allegorical and mystical subtleties after the manner of Philo and the Alexandrian school.
Unlike his contemporaries, he emphasizes the difference between the Hebrew Bible "apocrypha" and the Hebraica veritas of the protocanonical books.
In his Vulgate's prologues, he describes some portions of books in the Septuagint that were not found in the Hebrew as being non-canonical (he called them apocrypha); for Baruch, he mentions by name in his Prologue to Jeremiah and notes that it is neither read nor held among the Hebrews, but does not explicitly call it apocryphal or "not in the canon".
His Preface to The Books of Samuel and Kings includes the following statement, commonly called the Helmeted Preface:
This preface to the Scriptures may serve as a "helmeted" introduction to all the books which we turn from Hebrew into Latin, so that we may be assured that what is not found in our list must be placed amongst the Apocryphal writings.
Wisdom, therefore, which generally bears the name of Solomon, and the book of Jesus, the Son of Sirach, and Judith, and Tobias, and the Shepherd are not in the canon.
The first book of Maccabees I have found to be Hebrew, the second is Greek, as can be proved from the very style.

Although Jerome was once suspicious of the apocrypha, it is said that he later viewed them as Scripture.
For example, in Jerome's letter to Eustochium he quotes Sirach 13:2; elsewhere Jerome also refers to Baruch, the Story of Susannah and Wisdom as scripture.

Jerome's commentaries fall into three groups:
His translations or recastings of Greek predecessors, including fourteen homilies on the Book of Jeremiah and the same number on the Book of Ezekiel by Origen (translated c. 380 in Constantinople); two homilies of Origen of Alexandria on the Song of Solomon (in Rome, c. 383); and thirty-nine on the Gospel of Luke (c. 389, in Bethlehem).
The nine homilies of Origen on the Book of Isaiah included among his works were not done by him.
Here should be mentioned, as an important contribution to the topography of Palestine, his book De situ et nominibus locorum Hebraeorum, a translation with additions and some regrettable omissions of the Onomasticon of Eusebius.
To the same period (c. 390) belongs the Liber interpretationis nominum Hebraicorum, based on a work supposed to go back to Philo and expanded by Origen.

Original commentaries on the Old Testament.
To the period before his settlement at Bethlehem and the following five years belong a series of short, Old Testament studies: De seraphim, De voce Osanna, De tribus quaestionibus veteris legis (usually included among the letters as 18, 20, and 36); Quaestiones hebraicae in Genesim; Commentarius in Ecclesiasten; Tractatus septem in Psalmos 10–16 (lost); Explanationes in Michaeam, Sophoniam, Nahum, Habacuc, Aggaeum.
After 395 he composed a series of longer commentaries, though in rather a desultory fashion: first on Jonah and Obadiah (396), then on Isaiah (c. 395 – c. 400), on Zechariah, Malachi, Hoseah, Joel, Amos (from 406), on the Book of Daniel (c. 407), on Ezekiel (between 410 and 415), and on Jeremiah (after 415, left unfinished).

New Testament commentaries.
These include only Philemon, Galatians, Ephesians, and Titus (hastily composed 387–388); Matthew (dictated in a fortnight, 398); Mark, selected passages in Luke, Revelation, and the prologue to the Gospel of John.
For the next 15 years, until he died, Jerome produced a number of commentaries on Scripture, often explaining his translation choices in using the original Hebrew rather than suspect translations. His patristic commentaries align closely with Jewish tradition, and he indulges in allegorical and mystical subtleties after the manner of Philo and the Alexandrian school. Unlike his contemporaries, he emphasizes the difference between the Hebrew Bible "apocrypha" and the Hebraica veritas of the protocanonical books. In his Vulgate's prologues, he describes some portions of books in the Septuagint that were not found in the Hebrew as being non-canonical (he called them apocrypha); for Baruch, he mentions by name in his Prologue to Jeremiah and notes that it is neither read nor held among the Hebrews, but does not explicitly call it apocryphal or "not in the canon". His Preface to The Books of Samuel and Kings includes the following statement, commonly called the Helmeted Preface:
This preface to the Scriptures may serve as a "helmeted" introduction to all the books which we turn from Hebrew into Latin, so that we may be assured that what is not found in our list must be placed amongst the Apocryphal writings. Wisdom, therefore, which generally bears the name of Solomon, and the book of Jesus, the Son of Sirach, and Judith, and Tobias, and the Shepherd are not in the canon. The first book of Maccabees I have found to be Hebrew, the second is Greek, as can be proved from the very style.
Although Jerome was once suspicious of the apocrypha, it is said that he later viewed them as Scripture. For example, in Jerome's letter to Eustochium he quotes Sirach 13:2; elsewhere Jerome also refers to Baruch, the Story of Susannah and Wisdom as scripture.
Jerome's commentaries fall into three groups:
His translations or recastings of Greek predecessors, including fourteen homilies on the Book of Jeremiah and the same number on the Book of Ezekiel by Origen (translated c. 380 in Constantinople); two homilies of Origen of Alexandria on the Song of Solomon (in Rome, c. 383); and thirty-nine on the Gospel of Luke (c. 389, in Bethlehem). The nine homilies of Origen on the Book of Isaiah included among his works were not done by him. Here should be mentioned, as an important contribution to the topography of Palestine, his book De situ et nominibus locorum Hebraeorum, a translation with additions and some regrettable omissions of the Onomasticon of Eusebius. To the same period (c. 390) belongs the Liber interpretationis nominum Hebraicorum, based on a work supposed to go back to Philo and expanded by Origen.
Original commentaries on the Old Testament. To the period before his settlement at Bethlehem and the following five years belong a series of short, Old Testament studies: De seraphim, De voce Osanna, De tribus quaestionibus veteris legis (usually included among the letters as 18, 20, and 36); Quaestiones hebraicae in Genesim; Commentarius in Ecclesiasten; Tractatus septem in Psalmos 10–16 (lost); Explanationes in Michaeam, Sophoniam, Nahum, Habacuc, Aggaeum. After 395 he composed a series of longer commentaries, though in rather a desultory fashion: first on Jonah and Obadiah (396), then on Isaiah (c. 395 – c. 400), on Zechariah, Malachi, Hoseah, Joel, Amos (from 406), on the Book of Daniel (c. 407), on Ezekiel (between 410 and 415), and on Jeremiah (after 415, left unfinished).
New Testament commentaries. These include only Philemon, Galatians, Ephesians, and Titus (hastily composed 387–388); Matthew (dictated in a fortnight, 398); Mark, selected passages in Luke, Revelation, and the prologue to the Gospel of John.
Jerome