Bibliotheca a fundatore mazarinea : the inscription engraved upon the pediment of the main courtyard's eastern portico describes the purpose of this wing of the Palais de l'Institut and carries on the memory of its founder, Cardinal Mazarin whose arms decorate the tympanum and whose bust sculpted by Lerambert circa 1664-1669 is opposite the main courtyard.

   The Bibliothèque is accessible through a staircase built in 1824 by Léon Biet according to plans drawn up by Vaudoyer. Topped by an oval-shaped gallery decorated with antique busts and surmounted by a glass roof letting daylight pour in, this staircase marks a semi-oval curve lined with niched busts. Up the staircase, one reaches a landing and is faced with two monumental doors bearing the inscriptions Museum and Bibliotheca, engraved on black marble.

   Past the threshold, one enters a small coffered-ceiling octogonal room. The room is refered to as the Atrium colbertinum and is dedicated to the Library's Catalogs. The catalogs are contained partly in online catalog and partly in a card-catalog format whose indexed references are filed in the furniture placed in the centre of room as well as in the numerous drawers encased in the walls. Framed in red marble, decorated with white marble rosaces, the door leading to the main hall bears the inscription Mazarinaea.

  Upon entering the main hall or reading room, one can catch a glimpse of Mazarin's arms placed above a black marble plate that reads Salle Gabriel Naudé, linking the founder of the library to its mastermind Naudé.

        The reading room is 65 meters long with the entrance hall overlooking the Seine's embankment measuring 18 meters and the main gallery stretching out 47 meters. It is over 8 meters both in width and in height. It recreates the surroundings of the library in Mazarin's hôtel particulier, located on rue de Richelieu, and housed in a hall designed by architect Pierre le Muet (1591-1669) : in 1689 the entire library - that is the books and also the woodwork, columns, shelves, lecterns and balcony - was relocated in the eastern wing of the Collège des Quatre-Nations built according to plans drawn up by Le Vau. Fifty-four fluted corinthian order columns support a balcony whose bottom floor is adorned with fasces and stars as seen in Mazarin's arms. These columns punctuate the harmonious sequence of 18 bay-windows and 32 rows of shelving.

The reading room is decorated with works of art, furniture, antique and classical busts made of marble, bronze or terracotta placed on marble or alabaster pedestals most of which come from confiscations that occurred during the Revolution.

 

   In the small gallery, hang two rocaille-style chandeliers made of gilted and chased bronze. They belonged to the Marquise de Pompadour and are attributed to Caffieri the sculptor. It is said that the beautiful Louis XV style pendulum clock with its kingwood and rosewood marquetry stood in the study Louis XVI.

 

   At the far end of the main gallery lit by four Louis XIV style chandeliers and one designed by Boulle, one is struck in particular by two Louis XVI style mahogany credenze designed by Riesener, a celestial globe designed by Coronelli and a marble writing desk bearing Condé's arms that is said to have belonged to the victor of the battle of Rocroi.