The Diocese of Massa Marittima-Piombino (Latin: Dioecesis Massana-Plumbinensis) is a Roman Catholic eccleasistical territory in Tuscany, central Italy. It was known as Diocese of Massa Marittima before 1978. Up until 1458, it was a suffragan of the archdiocese of Pisa; since 1458, it has been a suffragan of the Archdiocese of Siena. The territory of the diocese includes the islands of Elba and Pianosa, and (up to 1817) Capraia.