Diego Ortiz (c. 1510 - c. 1570) was a Spanish composer and music theorist in service to the Spanish viceroy of Naples and later to Philip II of Spain. Ortiz published the first manual on ornamentation for bowed string instruments, and a large collection of sacred vocal compositions (Stevenson 2001).
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 cappella 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.
The Trattado de Glosas (modern Spanish spelling Tratado de Glosas) is considered a masterpiece of literature for the viola da gamba. The work was published on 10 December 1553, in Rome under the Spanish title Trattado de glossas sobre clausulas y otros generos de puntos en la musica de violones nuevamente puestos en luz. The Italian edition was published at the same time, with the title Glose sopra le cadenze et altre sorte de punti in la musica del violone. The Italian edition is full of Hispanicisms, which suggests that Ortiz made this version himself (Stevenson 2001).
Ortiz published a collection of polyphonic religious music in 1565 in Venice. Musices liber primus hymnos, Magnificas, Salves, motecta, psalmos includes sixty-nine compositions for four to seven voices, based on plainchant works. They are stylistically conservative for the period, appropriate to the tastes of the dedicatee, Ortiz's employer, Pedro Afán de Rivera, Duke of Alcalá and the Spanish Viceroy in Naples. In the preface to this publication, Ortiz encourages performers to accompany these sacred polyphonic works with instruments, a practice favoured at the time in Spain, and promises future publication of a book of masses which never appeared (Stevenson 2001).