Diego Ortiz was a Spanish composer and musicologist, in service to the Spanish viceroy of Naples and later to Philip II of Spain. Ortiz published influential treatises on both instrumental and vocal performance.
Very little is known about his life. He is believed to have been born in Toledo and died in Naples.
In 1553 Ortiz was living in the viceroyalty of Naples. Five years later, the third duke of Alba, Fernando Álvarez de Toledo, appointed him maestro di capella of the Chapel Royal of Naples. In 1565 Ortiz still held the post under the Viceroy Pedro Afán de Ribera, duke of Alcalá.
Ortiz published two music books: Trattado de Glosas in 1553 and Musices liber primus in 1565.