The Diocese of Tarazona (Latin: Dioecesis Turiasonensis) is a Latin diocese of the Catholic Church located in north-eastern Spain, in the provinces of Zaragoza, Soria, Navarre and La Rioja, forming part of the autonomous communities of Aragón, Castile-Leon, Navarre and La Rioja.

[1] The city of Tarazona is situated on a commanding point, surrounded by a beautiful open plain, through which the river Queiles flows.

It was endowed by Teresa Cajal, mother of Pedro de Atarés and wife of García Sánchez, and was begun in 1152.

Bishop Moncada attempted to rebuild the beautiful cloister which had been destroyed in the War of the Two Peters, but as late as 1529 this had not been completed.

Turiaso was one of the principal towns of the ancient Celtiberian province, and within the confines of the diocese are found many very ancient cities: Bilbilis (Calatayud); Aquae Bilbilitanorum (Alhama); Atacum (Ateca); Augustobriga (Muro); Boverca (Buvierca); Bursao (Borja); Cascantum (Cascante); Gracuris (Corella); Monóbriga (Munébrega); and Vergegium (Verdejo).

Owing to its proximity to Saragossa it is supposed that it was visited at an early date by the disciples of Saint James the Great, but until the 5th century there is no reliable mention of a bishop of Tarazona.

When the Moors took Tarazona they were able to hold it for a long time on account of its fortified position near the Sierra del Moncayo, between the Douro and the Ebro rivers.

The Council of Burgos, which was convened in 1139, and was presided over by the legate Guido, took from the jurisdiction of Tarazona most of the towns of Soria, but bestowed in its place the Archdeaconry of Calatayud.

In a species of national council held at Tarazona, the marriage of James to Leonor of Castile was declared null on account of the relationship existing between them.