Fabio Costantini was an Italian music editor and composer. He sang under Palestrina at St Peter's, Rome (until 1610), and held posts as maestro di cappella, notably at Orvieto Cathedral (1610-14, 1618-22), Santa Casa, Loreto, Ancona and Ferrara Cathedral. His anthologies of polyphonic psalms (with other liturgical music; six books, 1614-39) and concertato motets (four books, 1616-34, one lost) were important in the dissemination of early 17th-century Roman music. As a composer he preferred the concertato style; the motets contain some of his best music.
His brother Alessandro (c 1581-1657) succeeded Frescobaldi as organist of St Peter's in 1643; he also wrote concertato motets with a preference for duets and dialogues.