The Old Testament
Bible Books of the Old Testament are in tree Groups
17 Historical: Rise and Fall of the Hebrew Nation.
5 Poetical: Literature of the Nation's Golden Age.
17 Prophetic: Literature of the Nation's Dark Days.
The Hebrew Old Testament contains exactly the same books as our English Old Testament, but different arrangement:
"Law" (5 books) : Genesis, Exodus, Leviticus, Numbers, Deuteronomy.
"Prophets" (8 books): 4 Earlier: Joshua, Judges, Samuel, Kings / 4 Later: Isaiah, Jeremiah, Ezekiel, The Twelve.
"Writings" (11 books): 3 Poetical: Psalms, Proverbs, Job / 5 Rolls: Song, Ruth, Lamentations, Ecclesiastes, Esther. / 3 Books: Daniel, Ezra-Nehemiah, Chronicles.
By combining the 2 books each of Samuel, Kings and Chronicles into one, and Ezra and Nehemiah into one, and the Twelve Minor Prophets into one, these 24 books are the same as our 39. Josephus further reduces the number to 22, to make it correspond to the Hebrew alphabet by combining Ruth with Judges, and Lamentations with Jeremiah.
The five Rolls were read yearly at Feasts:
Song, at Passover, allegorically referring to the Exodus.
Ruth, at Pentecost, celebrating Harvest.
Esther, at Purim, commemorating Deliverance from Haman.
Ecclesiastes, at Tabernacles, most joyous of Feasts.
Lamentations, 9th of Ab, commemorating Destruction of Jerusalem.
The Septuagint Translators re-classified the Old Testament books according to subject-matter. English translators followed the Septuagint order, as we now have them.
(Halley's Bible Handbook. p 26)