The “Opera della Metropolitana di Siena” is one of the oldest Italian and European institutions. Since 1200, the Opera has an autonomous bureaucratic structure, a large real estate and also an administrative headquarters. 

Initially at the top of the administration, there was a Worker, then replaced in 1362 by a real treasurer (Camerlengo).

In 1545 at the top of the Opera was provided a Rector, elected by the highest city institutions and a council of nine "Savi".

In the last decades of 1700, the structure of the Opera was modified several times until in 1790 the Rector was entrusted with all administrative responsibilities. After the Unification of Italy, the Opera del Duomo di Siena was subjected, to the legislation of the unitary State.

Its places are composed of: Cathedral, Floor, Piccolomini Library, Panorama and New Cathedral, Museum, Crypt, Baptistery, Oratory of San Bernardino and Diocesan Museum of Sacred Art.