The Agnus Dei, the figure of a lamb bearing a cross, is a symbol of Jesus as the Lamb of God. The device is common in ecclesiastical art, but the name is especially given in the Church of Rome to a small cake made of the wax of the Easter candles and impressed with this figure. Since the 9th century, it has been customary for the Pope to bless these cakes, and distribute them on the Sunday after Easter among the faithful, by whom they are highly prized as having the power to avert evil. In modern times the distribution has been limited to persons of distinction, and is made by the Pope on his accession and every seven years thereafter.

"Agnus Dei" is also the popular name for the anthem beginning with these words, which is said to have been introduced into the Mass by Pope Sergius I (687-701). Based upon John i. 29, the Latin form is Agnus Dei, qui tollis peccata mundi, miserere nobis (Lamb of God, who takes away the sins of the world, have mercy on us). In the celebration of the Mass it is repeated three times before the communion, and it is also appended to many of the litanies. By the judgment in the case of Read and others v. The Bishop of Lincoln it was decided in 1890 that the singing of the "Agnus Dei" in English by the choir during the administration of the Holy Communion, provided that the reception of the elements be not delayed till its conclusion, is not illegal in the Church of England.

A translation of the anthem "Agnus Dei" may be found in the article Lamb of God (music).

"Agnus Dei" is also the name of Samuel Barber's choral arrangement of his Adagio for Strings.

"Agnus Dei" is also the name of a contemporary Christian praise song written by Michael W. Smith and performed by him and by Third Day