Dewey was a pioneer in American librarianship and an influential figure in the development of libraries in America in the late 19th and early the 20th century. He is best known for the decimal classification system that many public and school libraries use. Among his other innovations was the idea of a state library operating as the controller of the state's school and public library services. In Boston, Massachusetts, he founded the Library Bureau, a private company "for the definite purpose of furnishing libraries with equipment and supplies of unvarying correctness and reliability." Its investigative unit, devoted to studying the best practices of library loss-management, circulation and data retention, recovered 3,000 books in its first year of existence. Dewey's Library Bureau company is also said to have introduced hanging vertical files, first seen at the Columbian Exposition of 1893 in Chicago. In 1905, Dewey established the American Library Institute which was an organization conceived to provide for the investigation, study and discussion of issues within the field of library theory and practice.
Another biography refers to Dewey's "old nemesis—a persistent inability to control himself around women" as a chronic cause of trouble on the job. For decades, Dewey engaged in "unwelcome hugging, unwelcome touching, certainly unwelcome kissing" with female subordinates and others, according to biographer Wayne A. Wiegand. When Dewey opened his School of Library Economy at Columbia College to women it was rumored that he asked for their bust sizes with their applications. Though the rumor turned out to be false he did require a photograph from each female applicant since "you cannot polish a pumpkin". In 1905 during a 10-day trip to Alaska sponsored by the American Library Association (ALA), a group he co-founded, he made unwelcome advances on four prominent librarians who informed Association officials. As a result, Dewey stepped down from active participation in the ALA. Reports, allegations, and an investigation of Dewey's inappropriate and offensive behavior directed at women continued for decades after his departure from ALA. In 1930, he paid $2,000 to settle a lawsuit by a former secretary alleging sexual harassment.