Adon Olam (Lord of the world, or eternal Lord) is a short metrical Hebrew hymn on the eternity, unity and providence of God, sung at the conclusion of the Sabbath and festival morning service and, in many communities, at the opening of the daily morning prayers and as a bedtime prayer. Its verses declare that God reigned before all creation and will reign when all has ended, that he is one without compare, and that the worshipper commits their spirit into his hand in sleep and waking, fearing nothing because God is with them. Of uncertain authorship and medieval date, sometimes attributed to the eleventh-century poet Solomon ibn Gabirol, it has been set to a great many tunes and is among the best-known and most-sung of synagogue hymns. Its combination of an exalted theology of the eternal and singular God with an intimate expression of personal trust has given it an enduring place in both public worship and private devotion across the Jewish world.
Its final stanza, in which the worshipper commits their spirit into God's hand and declares that they will not fear because the Lord is with them, closely echoes the wording of Psalm 31, and this borrowing has led some scholars to see the hymn as a deliberate liturgical elaboration on that verse rather than a wholly independent composition. The sheer number of melodies written for Adon Olam, spanning traditional synagogue chant, folk tunes and even contemporary popular settings, has made it something of a musical showcase within Jewish worship, with some congregations rotating among several tunes across a single year.