Hallel (praise) is a unit of psalms, Psalms 113 to 118, recited as a group on the festivals and the new moons, sung standing as an act of thanksgiving and praise. These psalms celebrate God's deliverance of Israel, above all the exodus from Egypt, and his kingship and faithfulness, and their recitation marks the joyful days of the calendar; the tradition distinguishes a full and an abbreviated form, the shorter being used on occasions of lesser joy or where full rejoicing is tempered, as on the later days of Passover. On the night of the Passover Seder the Hallel is divided around the meal, and it is closely associated with the great pilgrimage festivals. Its use gives the festivals their character of communal rejoicing before God, the congregation joining in ancient songs of praise and gratitude for redemption. The Talmud discusses its recitation and origins, and it has remained a fixed and joyful element of festival worship across the Jewish world.
The Mishnah records a dispute among the sages over exactly when in Jewish history the custom of reciting these particular psalms as a fixed unit began, some tracing it to the prophets and elders of the Second Temple period and others to Moses and the Israelites at the parting of the sea, a disagreement preserved in the Talmud rather than resolved by it. The distinction between full and partial Hallel, and the specific festival days assigned to each, remains a matter of variation between communities, particularly around the intermediate days of Passover, and prayer books differ in exactly how they mark the shortened form.