Psalms
The Psalter (also known as the Psalms of David) is the Old Testament book that contains hymns and poems traditionally ascribed to the Holy Prophet and King David, ancestor of our Lord Jesus Christ. Virtually every aspect of worship—praise, thanksgiving, penitence, intercession—is covered in the Psalter.
See also:
Daily Readings from the Orthodox Psalter
Kathisma
Septuagint Numbering of Psalms