Louis XVI’s library at Versailles is the only room in the Private Apartments (Petits appartements) that the unfortunate monarch substantially altered after he came to the throne. Otherwise, he left his grandfather Louis XV’s rooms more or less as he found them.
Consequently, this library is also the only room in the Private Apartments that is decorated in the neo-classical style to which Louis XVI has given his name. Note the rectilinear paneling in the picture below.
Louis XV had of course also had a library. In fact, he had several. A series of small libraries in the attic-level Petits cabinets was constructed for him in the 1730s, including a map room. He lost interest in the Petits cabinets after the creation of the Private Apartments and eventually made them over to his daughter-in-law, the Dauphine, in 1766. After her death, they passed to Mme du Barry, for whom an exquisite little library was arranged. It can be visited today.