Psalms is the 19th book of the Old Testament and the 2nd book of poetry. It has 150 chapters. In the Hebrew Bible, Psalms is part of the כְּתוּבִים (Ketuvim, or Writings).
The Psalms were written over a wide span of time. The earliest, Psalm 90, was written by Moses some time around 1500 BC, while some of the last were written after the Exile, around 500 BC. Most of the Psalms, however, were written during and around the time of King David (the author of at least seventy-three), from 1030 to 930 BC. The Psalms were probably compiled into a single book by an editor, likely Ezra.