The Old Testament is the part of the Bible that was written prior to the time of Jesus Christ.
However, if you had been around to ask the apostles John, Peter or Paul about the “Old Testament” they would have had no idea what you meant. The terms Old Testament and New Testament were coined long after the books of the Bible were written. In 2 Tim 3:15-16, the apostle Paul referred to the Old Testament writings as the holy scriptures, given by the inspiration of God.
What we today call the Old Testament is the older part of the body of evidence claimed to be God's works and His communications to mankind as written down by its mostly Israelite authors. The Old Testament books were written in Hebrew with the exception of some parts of the books of Ezra and Daniel that were written in Aramaic, a language close to Hebrew. The Aramaic portions in the Old Testament include Daniel 2:4b to 7:28 and Ezra 4:8—6:18, 7:12-26.
The canon of Old Testament books, as recognised by western Protestant churches, consists of 39 books. Most Protestant churches recognise only the same Old Testament books that Judaism recognises as part of their scriptural canon. The Roman Catholic and Eastern Orthodox churches recognise additional apocryphal books.
The Jews combined a number of the Old Testament books and recognised 22 books within their three-fold division of the Old Testament which they refer to as the Tanakh (derived from a Hebrew acronym of the three divisions).
The Jews grouped the Old Testament books into 3 divisions referred to as the 1) Law of Moses (or the Torah), 2) the Prophets and 3) the Writings (or the Psalms). Jesus Christ referred to this three-fold division in Luke 24:44. The books of their three-fold division are as follows:
I. THE LAW (Torah)
1) Genesis
2) Exodus
3) Leviticus
4) Numbers
5) Deuteronomy
II. THE PROPHETS (Nevi'im)
6) Joshua and Judges
7) The Book of Kingdoms (1 and 2 Samuel and 1 and 2 Kings)
8) Isaiah
9) Jeremiah
10) Ezekiel
11) The Twelve (Hosea to Malachi)
[always reckoned as one book by the Jews]
III. THE HOLY WRITINGS (Ketuvim)
(or THE PSALMS because it was the first book in the collection in this “Royal Division”)
12) The Psalms
13) The Proverbs
14) Job
15) Song of Songs
16) Ruth
17) Lamentations
18) Ecclesiastes
19) Esther
20) Daniel
21) Ezra-Nehemiah [reckoned as one book by the Jews]
22) The Book of Chronicles [reckoned as one book by the Jews]