Vatican Library

The Vatican Apostolic Library (Latin: Bibliotheca Apostolica Vaticana), more commonly called simply the Vatican Library, is the library of the Holy See, currently located in Vatican City. It is one of the oldest libraries in the world and contains one of the most significant collections of historical texts. Formally established in 1475, though in fact much older, it has 75,000 codices from throughout history. From July 2007, the library had been temporarily closed to the public for rebuilding, and reopened in September 2010.

More information on the Wikipedia page

The website, in Italian and English, is.