Charles Ammi Cutter (14 March 1837–6 September, 1903) is an important figure in the history of American library science.
Cutter was appointed assistant librarian of Harvard Divinity School while still a student there. After graduation, Cutter worked as a librarian at Harvard College, where he developed a new form of index catalog, using cards instead of published volumes, containing both an author index and a "classed catalog" or a rudimentary form of subject index.
In 1868 Cutter was appointed librarian of the Boston Athenaeum.
Cutter's most significant contribution to the field of library science was the development of the Expansive Classification system. This system influenced the development of the Library of Congress.
As part of his work on this system, he developed a system of alphabetic tables used to abbreviate authors' names. This system of numbers ("Cutter numbers") is still used today in libraries.
Cutter was one of the 100 or so founding members, in 1876, of the American Library Association.
Charles Cutter was born in Boston, Massachusetts and died in Walpole, New Hampshire.