The Psalms are arranged into five books: Book 1 (Psalms 1‑41); Book 2 (Psalms 42‑72); Book 3 (Psalms 73‑89); Book 4 (Psalms 90‑106); and, Book 5 (Psalms 107‑150). Each of the five books concludes with a doxology, signifying the completion of the collection. For example, Psalm 41:13 ends Book 1: “Blessed be the Lord, the God of Israel, from everlasting to everlasting. Amen and Amen.” The entire Psalm 150 serves as the final doxology to the entire Psalter.