The library is one of the largest buildings in the world devoted entirely to rare books and manuscripts, the library has room in the central tower for 180,000 volumes and in the underground book stacks for over 600,000 volumes; it now contains about 500,000 volumes and several million manuscripts.

The library contains five major collections: the General Collection of Rare Books and Manuscripts, the Collection of American Literature, the Collection of Western Americana, the German Literature Collection, and the Osborn Collection of English literary and historical manuscripts.

On permanent exhibition in cases on the mezzanine are the Gutenberg Bible, the first Western book printed from movable type, and Audubon's Birds of America. Special exhibitions are arranged throughout the year.