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.

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.

In 1839, Alexandre Vattemare, a French philanthropist, suggested that all of Boston's libraries combine into one institution for the benefit of the public.

At Vattemare's urging, Paris sent gifts of books in 1843 and 1847 to assist in establishing a unified public library.

Indirectly, John Jacob Astor, businessman and philanthropist, also influenced the establishment of a public library in Boston.

In May 1852 the city council adopted the recommendations of the mayor and Edward Capen was chosen to become Boston Public Library's first librarian.

The opening day collection of 16,000 volumes fit in the Mason Street building, but it quickly became obvious that its quarters were inadequate.

Designed by Charles Kirk Kirby to hold 240,000 volumes, the imposing Italianate edifice opened in 1858.

With the aim of increasing its reach throughout the city and providing services to residents everywhere, the library opened 21 more branches in Boston neighborhoods between 1872 and 1900.

In 1888, Charles Follen McKim proposed a Renaissance style design based on the Bibliothèque Ste-Geneviève in Paris.

The principles in the plan and all of the related outcomes were the result of a two-year community engagement process for which Boston Public Library received national recognition.

The second phase of the Johnson building renovations opened in the summer 2016 and included the first floor, mezzanine, and exterior.

The central library as a whole with the two buildings combined contains 930,000 square feet (86,000 m2) of space and houses 21 million items in its collections as of 2015.

[30] Designed by Philip Johnson, this late modernist addition, which predated postmodernist architecture, was built in 1967–1971 and opened in 1972.

Upon opening, the Johnson building became the home for the Boston Public Library's main circulating collection, which includes works in many languages.

[31] The Boston Public Library hosts thousands of free public programs each year, including Author Talks, Local and Family History lectures, the Lowell Lecture Series, Concerts in the Courtyard, and art and history exhibitions.

[32][33] The Boston Public Library also offers many daily events for children, teens, adults, and seniors, including story times, therapy dog story times,[34] book discussions, film showings, ESL conversation groups, and research and technology classes.

Plug-in Ethernet access is also available in the McKim building's Bates Hall and the Honan-Allston Branch's Adult Reading Room for up to 2 hours.

The online catalog, also available for mobile devices, allows users to browse and place holds on materials including books, audiobooks, DVDs, and CDs.

Users can also download ebooks, e-audiobooks, music, and video through BPL's OverDrive site and check out Zinio magazines for the computer, tablet, or smartphone.