The British Library, the national library of the United Kingdom.

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The British Library (BL) is the national library of the United Kingdom. It is based in London and is one of the world's largest research libraries, holding over 150 million items in all known languages and formats; books, journals, newspapers, magazines, sound and music recordings, patents, databases, maps, stamps, prints, drawings and much more. Its book collection is second only to the American Library of Congress. The Library's collections include around 25 million books,[2] along with substantial additional collection of manuscripts and historical items dating back as far as 300 BC.

from Wikipedia - The British Library