According to its website, the Boston Public Library has a collection of over 23.7 million items, which makes it one of the largest municipal public library systems in the United States. The vast majority of the collection – over 22.7 million volumes — is held in the Central Branch research stacks. Between July 2012 and June 2013, the annual circulation of the BPL was 3.69 million. Because of the strength and importance of its research collection, the Boston Public Library is a member of the Association of Research Libraries (ARL), a not-for-profit organization comprising the research libraries of North America. The New York Public Library is the only other public library that is a member of the ARL. The library has established collections of distinction, based on the collection’s depth and breadth, including subjects such as Boston history, the Civil War, Irish History, etc. In addition, the library is both a federal and state depository of government documents.
Included in the BPL’s research collection are more than 1.7 million rare books and manuscripts. It possesses wide-ranging and important holdings, including medieval manuscripts and incunabula, early editions of William Shakespeare (among which are a number of Shakespeare quartos and the First Folio), the George Ticknor collection of Spanish literature, a major collection of Daniel Defoe, records of colonial Boston, the personal 3,800 volume library of John Adams, the mathematical and astronomical library of Nathaniel Bowditch, important manuscript archives on abolitionism, including the papers of William Lloyd Garrison, and a major collection of materials on the Sacco and Vanzetti case. There are large collections of prints, photographs, postcards, and maps. The library, for example, holds one of the major collections of watercolors and drawings by Thomas Rowlandson. The library has a special strength in music, and holds the archives of the Handel and Haydn Society, scores from the estate of Serge Koussevitzky, and the papers of and grand piano belonging to the important American composer Walter Piston.
For all these reasons, the historian David McCullough has described the Boston Public Library as one of the five most important libraries in America, the others being the Library of Congress, the New York Public Library, and the university libraries of Harvard and Yale.