The Hapgood, M.D., mss., 1912-1975, consists of the correspondence and writings of Socialist leaders Mary Donovan Hapgood, 1886-1973, and Powers Hapgood, 1899-1949.
The Sinclair mss. VI, 1907-1977, consists of correspondence, writings, and miscellaneous papers by and relating to author Upton Beall Sinclair, 1878-1968, his wife Mary Craig (Kimbrough) Sinclair, 1882-1961, and his son David Sinclair, 1901-1987.
The Sinclair mss. V, 1902, consists of the application of novelist Upton Beall Sinclair, 1878-1968, for a fellowship in the Graduate School of Harvard University for the year 1902-1903.
The U.S. History mss., 1612-1977, consist of individual items acquired separately either as a gift, purchase, transfer, or removal from a variety of sources, relating to the United States. Additions continue to be made.