The Biblioteca Nacional is Spain's highest library institution and is head of the Spanish Library System.

As the country's national library, it is the centre responsible for identifying, preserving, conserving, and disseminating information about Spain's documentary heritage, and it aspires to be an essential point of reference for research into Spanish culture. In accordance with its Articles of Association, passed by Royal Decree 1581/1991 (R.D. 1581/1991) of 31 October 1991, its principal functions are to:

• Compile, catalogue, and conserve bibliographic archives produced in any language of the Spanish state, or any other language, for the purposes of research, culture, and information.
• Promote research through the study, loan, and reproduction of its bibliographic archive.
• Disseminate information on Spain's bibliographic output based on the entries received through the legal deposit requirement.

The library's collection consists of more than 26,000,000 items, including 15,000,000 books and other printed materials, 4,500,000 graphic materials, 600,000 sound recordings, 510,000 music scores, more than 500,000 microforms, 500,000 maps, 143,000 newspapers and serials, 90,000 audiovisuals, 90,000 electronic documents, and 30,000 manuscripts.

The current director of the Biblioteca Nacional is Ana Santos Aramburo, appointed in 2013. Former directors include her predecessors Glòria Pérez-Salmerón (2010–2013) and Milagros del Corral (2007-2010) as well as historian Juan Pablo Fusi (1996–2000) and author Rosa Regàs (2004–2007).

Given its role as the legal deposit for the whole of Spain, since 1991 it has kept most of the overflowing collection at a secondary site in Alcalá de Henares, near Madrid.

The Biblioteca Nacional provides access to its collections through the following library services:

• Guidance and general information on the institution and other libraries.
• Bibliographic information about its collection and those held by other libraries or library systems.
• Access to its automated catalogue, which currently contains close to 3,000,000 bibliographic records encompassing all of its collections.
• Archive consultation in the library's reading rooms.
• Interlibrary loans.
• Archive reproduction.

• Stairs and main entrance with monuments to San Isidoro, Alonso Berruguete, Alfonso X el Sabio by José Alcoverro
• Statue of Hispania by Agustí Querol above the library
• A page from the manuscript of The Lay of the Cid
• Statue of Marcelino Menéndez y Pelayo in the lobby of the B.N.E.
• Building of the National Library of Spain in Alcalá de Henares