Diego Ortiz (c. 1510 – c. 1570) was a Spanish composer and musicologist, in service to the Spanish viceroy in Naples (Pedro de Urries) and later to Philip II of Spain. Ortiz published influential treatises on both instrumental and vocal performance.
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.
Trattado de Glossas 
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 punctos en la musica de violones nuevamente puestos en luz. Its Italian title is Glose sopra le cadenze et altre sorte de punti in la musica del violone.
Musices liber primus 
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.
- El primo(-secondo) libro de Diego Ortiz (click "View options" JPG icon) - Biblioteca Nacional de España info
- Free scores by Diego Ortiz in the Choral Public Domain Library (ChoralWiki)
- Free scores by Diego Ortiz at the International Music Score Library Project