The Hughes, Ted mss. II, 1957-1962, consist of letters from poet Ted Hughes, 1930-1998, and poet Sylvia Plath, 1932-1963, to Hughes' brother and sister-in-law, Gerald and Joan Hughes.
The Kopp mss., 1955-1958, consists of correspondence and memorabilia relating to author Sylvia Plath's time at Cambridge, collected by her friend Jane Kopp.
The Plath mss. IX, ca. 1972-2012, consists of correspondence between Aurelia Plath (Sylvia Plath's mother) and Olive Clifford Eaton (a neighbor in Winthrop, MA), Mary Alice Ericson (Olive Eaton's daughter), and Margery DeLerno (Olive Eaton's daughter).