Giovanni Maria Trabaci (ca. 1575 - 31 December 1647) was an Italian composer and organist. He was a prolific composer, with some 300 surviving works preserved in more than 10 publications; he was especially important for his keyboard music.
Trabaci was born in Monte Pelusio (now Irsina, near Matera). Nothing is known about his early life. On 1 December 1594 he was appointed tenor at Santissima Annunziata Maggiore in Naples, but already in 1597 he must have been known as an organist and organ expert, because he was invited that year to test the organ of Oratorio dei Filippini. He served as organist there for a while, and then became, in 1601, organist to the Spanish viceroys at the Chapel Royal of Naples. The second organist was Ascanio Mayone, and Giovanni de Macque was maestro di cappella. Trabaci succeeded Macque in 1614 after the latter's death, and held the post for the rest of his life. Between 1625 and 1630 he also worked at the Oratorio dei Filippini.
Trabaci was most noted for his keyboard works, which include ricercares, canzonas and toccatas collected in two publications. His bold harmonic language, with unexpected modulations to distant keys, and experiments with structure in these works influenced Girolamo Frescobaldi. He also wrote numerous sacred vocal works, but these are, in general, more conservative. His 1602 book of motets, Motectorum, features advanced harmonic writing and may have influenced Carlo Gesualdo's 1603 Sacrae cantiones.