The Book of Psalms, also known as the Psalter or the Psalms of David, is the Old Testament collection of sacred hymns, prayers, and poems traditionally associated with the Holy Prophet and King David, the ancestor of our Lord Jesus Christ.
The Psalter expresses virtually every aspect of the spiritual life and worship of God. Its prayers and hymns include praise and thanksgiving, repentance and penitence, supplication, intercession, and trust in God. Through the Psalms, the faithful give voice to both the joys and struggles of human life while continually turning toward God.
Because of its richness and variety, the Psalter has a central place in the worship and prayer of the Church, providing words through which the faithful can praise God, seek His mercy, give thanks for His blessings, and pray for themselves and others.
See also:
Daily Readings from the Orthodox Psalter
Kathisma
Septuagint Numbering of Psalms