Correspondence, diaries, essays and other writings, reports, notes, police and prison records, code books, criminal rosters, exhibition texts, legal documents, biographical and genealogical records, procedural guidelines and training manuals, financial records, card indexes, photographs, reward notices, wanted posters, illustrations, maps, and other records chiefly documenting the work of the private detective agency for clients in business and industry. Includes papers of Pinkerton family members who led the agency, Allan (1819-1884), Allan's sons William A. (1846-1923) and Robert A. (1848-1907), Robert's son, Allan (1876-1930), and Allan's son, Robert A. (1904-1967). Also includes papers of George H. Bangs, longtime general superintendent of the New York office.

Documents investigative methods, business principles and practices, and daily business activities. Topics include establishment by Pinkerton of the secret service in 1861 to protect the president and provide military intelligence for the Army of the Potomac, sabotage and espionage in the Washington, D.C., area during the Civil War, labor unrest and unionization in the Pennsylvania coal region, reports of James P. McParland in the investigation of the Molly Maguires, homeland security during World War I, the William J. Burns International Detective Agency, and criminals including Herman Mudgett, Butch Cassidy, and the Sundance Kid.