The book of Psalms is the longest book of the Bible, with 150 “chapters”—more properly called “psalms” or “songs.” Psalms is divided into five books
 
It is uncertain why Psalms is divided into five books. Some sources, including Jewish Midrash traditions, suggest the five-fold division is based on the five books of the Torah (Genesis to Deuteronomy). The division of the Psalms is not based on authorship or chronology, as several authors composed Psalms, and their individual songs are mixed throughout the various collections.