How Does the Book of Psalms Fit in the Bible?

In modern Christian Bibles, Psalms is the second book in the books of Poetry section (following Job). This organization of Law (Genesis–Deuteronomy); History (Joshua–Esther); Poetry (Job–Song of Songs); and Prophets (Isaiah–Malachi) is derived from the tradition of categorizing the biblical books adopted by Hellenistic Jewry and reflected (with some differences) in the Septuagint (the earliest Greek translation of the OT).

In manuscripts of the Hebrew Bible, Psalms is located in the section known as the Writings (or Hagiographa), the third and last division of the Hebrew Bible. The Hebrew Scriptures are divided into three sections: Torah (Genesis–Deuteronomy), the Prophets (Isaiah–Malachi) and Writings (Psalms, Proverbs, Job, Song of Songs, Ruth, Lamentations, Ecclesiastes, Esther, Daniel, Ezra–Nehemiah, Chronicles). Though the traditional place of Psalms in this third division varies between first (the modern Jewish consensus) and second (after Ruth or Chronicles), it is universally treated (as also in Christian tradition) as a distinct subgroup together with the two successive books of Proverbs and Job.

The prominent place of Psalms in the organization of the Hebrew canon is also evident in Luke 24:44, where, most likely because of its size, “the Psalms” is probably intended as a reference to the entire third division of the Writings (a figure of speech known as synecdoche, substituting a part for the whole). A similar reference—which is also highly significant as a testimony to the early canonization of the OT (earlier, at least, than many modern scholars have been prone to believe)—is also now known from a period more than 100 years before the previously cited reference by Luke, in one of the Dead Sea Scrolls, where the Scriptures are referred to as “the book of Moses and the books of the Prophets and (the Psalms of) David” (4QMMT, C 10).