The Appleton-Century mss., 1846-1962, consists of the office files of the publishing company, its two predecessors, D. Appleton & Co., and the Century Co., and to a small extent its successor, Appleton-Century Crofts, Inc.
The Armour mss., 1952-1956, consists of letters from author Upton Sinclair, 1878-1968, to author and English professor Richard Willard Armour, 1906-1989.
The Boni mss., 1926-1939, consists of the correspondence of author Upton Beall Sinclair, 1878-1968, with publishers Albert Boni, 1892-1981, and Charles Boni, 1894-1969.
The Cane mss., 1936-1957, consist of letters from Upton Sinclair, 1878-1968, author, to Melville Henry Cane, 1879-, lawyer and poet. They relate in the main to Sinclair's writings.
The Clark mss., 1909-1957, consists of the letters and writings of author, editor, and publisher Thomas Curtis Clark, 1877-1953, as well as the autographs and poems of other writers collected by him.
The Colorado-Sinclair mss. consists of letters exchanged between author, Upton Beall Sinclair, 1878-1968, and University of Colorado Director of Libraries Eugene Holt Wilson, 1909-?, Boulder, Colorado, August 25-October 31, 1950.
The DeWitt mss., 1941-1955, consists of letters from Upton Sinclair, 1878-1968, author, to Samuel Aaron DeWitt, 1891-1963, poet and businessman, and correspondence between Mary Craig (Kimbrough) Sinclair, (Mrs. Upton Sinclair), 1883-1961, and DeWitt.
The Eeden mss. consists of two reels, 1908-1913 and 1914-1918, of negative microfilm of letters and postcards of Upton Beall Sinclair, 1878-1968, novelist, to Frederik Willem van Eeden, 1860-1932, poet and dramatist, from the originals in the Frederik van Eeden-Genootschap at the University of Amsterdam in Amsterdam, Holland.
The Ehrmann mss., 1899-1926, consists of letters to Max Ehrmann, 1872-1945, author, from Eugene Victor Debs, Frank Harris and Upton Beall Sinclair, and Mrs. A. Schember.
The Engs, Ruth mss., 2001-2010, consist of typescripts, page proofs, correspondence, and research materials for works by health reform scholar Ruth Engs.
The Haldeman mss., 1948-1960, consists of files from Haldeman-Julius Publications of Girard, Kansas, containing correspondence with and book sales records of writer Upton Beall Sinclair, 1878-1968.
The Haldeman mss. II, 1908-1951, consists of correspondence of writers and editors, including Emanuel Haldeman-Julius, 1889-1951, who were connected to Haldeman-Julius Publications.
The Haldeman mss. III, 1915-1918, consists primarily of correspondence of Upton Beall Sinclair, 1878-1968, novelist, and Appeal to Reason staff members Louis Kopelin, 1887-1949, and Walter H. Wayland, 1884-1980.