The Museum is situated on the north eastern side of the square (at number 8), in a building that was created especially for the Opera del Duomo, or rather, the large number of administrators, artists and craftsmen (stone cutters, marble workers, carpenters...) who were employed in the construction of the new cathedral of Santa Maria del Fiore, which was commissioned in 1296. The Wool Guild, from whom the Opera took its coat of arms with the Agnus Dei, supervised the entire organization (from 1331 to 1770). Some of the crushing costs of the basilica were covered by the sale of wood from the forests of the Casentino, which the government of the Florentine Republic donated to the Opera in the late 14th century.
The institution therefore needed plenty of space: apart from the actual building site, it needed to be able to store all the huge uncut blocks of marble, as well as all the stacks of wood for sale. The palace we can see today was built over an earlier farmhouse and its land, purchased in 1400, which backed on to Lorenzo Ghiberti's workshop and furnaces (where the artist cast his bronze doors for the Baptistery). Donatello's workshop also stood in the vicinity, on the corner of Via Ricasoli. Filippo Brunelleschi was assigned the site for the new palace in 1432 but only the courtyard of this building, situated in front of the Museum entrance and subsequently altered several times, can still be seen today.

Once the basilica was completed, the Opera stayed open for the care and maintenance of the holy group of buildings, composed of the Duomo, the Baptistery and the Belltower and, after 1891, also opened some of its rooms to the public, transforming them into a Museum (architect Luigi Del Moro).
In fact a great many masterpieces from the three monuments, together with various historic reminders connected with the actual construction of Santa Maria del Fiore, like Brunelleschi's model for the cupola, the numerous 16th-17th century projects for the facade and pieces of building equipment (winches, trolleys, ropes...), had gradually been collected here over the centuries.

The first art works to be brought to the seat of the Opera were pieces of sculpture from the north door of the Cathedral (known as the Door of the Mandorla), among them an Annunciation created by Jacopo della Quercia for the lunette, replaced in 1491 with a mosaic by Ghirlandaio of the same subject. These were followed by the sculptures created by Arnolfo di Cambio, Nanni di Banco and Donatello (among others) for the first facade of Santa Maria del Fiore, which was left unfinished and "dismantled" in 1587 at the orders of Grand Duke Francesco I de' Medici.
The statues of Pope Boniface VIII and the Madonna and Child (1296) by Arnolfo are particularly beautiful, while the St. John the Evangelist was one of Donatello's first masterpieces (1408-15).

The beautiful Choir Lofts by Donatello (1433-38) and Luca della Robbia (1431-35), carried out as headpieces for the two sacristies in the Cathedral and dismantled in 1688 for the wedding of the Grand Prince Ferdinando with Violante of Baveria, were brought to the Opera even later: this was when people suddenly began to realise that care must be taken not to lose such valuable artifacts as these elsewhere.
They were followed by the sculptures carried out by Baccio Bandinelli from 1547-72 to close off the Cathedral Chancel and "disassembled" in 1842.

In this century, apart from the two Roman sarcophagi that stood on either side of the South Door of the Baptistery until 1971, the Museum has given shelter to the various masterpieces that have been restored over the years: these include the: Magdalen in wood by Donatello (from the Baptistery), sixteen statues by Donatello (note the Prophet Abacuc), Andrea Pisano and Nanni di Bartolo (from the Belltower), the bas-reliefs in marble by Giotto (?), Andrea Pisano, Alberto Arnoldi and Luca della Robbia (from the Belltower) and even the panels for the Door of Paradise by Ghiberti. All these bas-reliefs, statues and panels have today been replaced by copies.

The priceless Altar of San Giovanni comes from the interior of the Baptistery: composed of 400 kilos of silver, it was created between 1366 and 1480 by artists like Michelozzo, Verrocchio, Antonio del Pollaiolo and Bernardo Cennini.
A real monument to Florentine silversmithery, half Gothic and half Renaissance, which was commissioned by the Guild of Merchants (or "Calimala") and cost over 40.000 gold florins at the time (we should remember that Ghiberti was paid 4.000 florins for the North Doors in the same period).

The Pietà by Michelangelo comes instead from the Cathedral (the Magdalen is by one of his pupils, Tiberio Calcagni); the artist carried out this sculpture for his funerary chapel in Santa Maria Maggiore in Rome between 1548-55 but left it unfinished because of the poor quality of the marble, previously used for a capital in the Temple of Peace.
He gave it to his friend, Francesco Bandini, and the statue was sold to the Medici Grand Dukes by the Bandini heirs in the mid 17th century. It was at first placed in the crypt in San Lorenzo then, after 1721, behind the high altar in the Cathedral and lastly, from 1933, in the left transept, where it remained until 1980.

As we can see, these are a series of masterpieces that provide a complete panorama of the development of Florentine sculpture from the 14th to the 16th centuries. The Museum also contains a large number of Roman remains which were reutilized in the construction of the two temples, sculptures and bas-reliefs of all kinds and a huge collection of religious art (reliquaries, crosses, caskets, chasubles, croziers...).
One room in particular is dedicated to a display of the 58 illuminated Choir books that were in use in the cathedral until 1930: graduals, antiphonaries and vesperals, carried out on parchment between 1508 and 1530 but unfortunately seriously damaged in the flood of 1966.