Domenico Allegri (c. 1585 – 5 September 1629) was an Italian composer and singer of the early Baroque Roman School. He was the second son of the Milanese coachman Costantino Allegri, who lived in Rome with his family, and was a younger brother of the more famous Gregorio Allegri. Costantino sent three sons, Gregorio, Domenico and Bartolomeo, to study music at San Luigi dei Francesi, under the maestro di capella Giovanni Bernardino Nanino, brother of Giovanni Maria Nanino. The little boy had as schoolmate his elder brother Gregorio and then Antonio Cifra, Domenico Massenzio and Paolo Agostini.
In 1606, Allegri was maestro di cappella of the church of Santa Maria at Spello, and from September 1609 until April 1610 served in the same role at the church of Santa Maria in Trastevere in Rome. From 3 April 1610 until his death, he held the same position at the Basilica di Santa Maria Maggiore, where he was buried.
Allegri is mainly famous as being one of the first to include specific instrumental accompaniments to sacred vocal music on a small scale. While much of his music is lost, one piece which has survived is the Modi quos expositis in choris of 1617 which has accompaniments to the voices by two violins.