The Diocese of Grosseto (Latin: Dioecesis Grossetana) is a Latin Church diocese of the Catholic Church in Italy, a suffragan of the archdiocese of Siena-Colle di Val d'Elsa-Montalcino, in Tuscany.

[3] In January 591, Pope Gregory I appointed Balbinus, Bishop of Rusellæ, to be the Apostolic Visitor to the diocese of Populonia.

[6] A diocesan synod was an irregularly held, but important, meeting of the bishop of a diocese and his clergy.

Its purpose was (1) to proclaim generally the various decrees already issued by the bishop; (2) to discuss and ratify measures on which the bishop chose to consult with his clergy; (3) to publish statutes and decrees of the diocesan synod, of the provincial synod, and of the Holy See.

[8] On 14–15 April 1692, Bishop Cesare Ugolini (1665–1699) presided over a diocesan synod in Grosseto, and issued statutes which were published.