Collections for the twentieth and 21st centuries are focused on the first half of the twentieth century, withs some exceptions for materials which overlap with other collecting areas in the Library. Areas of strength in the twentieth- and 21st-century collections include:
H. E. (Herbert Ernest) Bates, 1905-1974: Nearly ninety editions of works, and a small collection of five letters by Bates.
Brigid Brophy, 1929-1995: The Library holds Brophy's annotated copies of Sigmund Freud's works, and an untitled manuscript by her on telepathy.
John Buchan, 1875-1940: Over 200 editions of works by Buchan, a virtually comprehensive collection of works published in his lifetime.
Joseph Conrad, 1857-1924: The Joseph Conrad Papers in the Rubenstein Library contain personal and professional correspondence by Conrad, some manuscripts and photographs, and a series of scrapbooks created by Conrad's wife Jessie. Additional Conrad letters may be found in the Library's Francis Warrington Dawson Papers. Scholarship about Conrad, and copies of his correspondence, are found in the William Blackburn Papers and Dale B.J. Randall Papers. In addition, there are approximately 75 editions of Conrad's works, including many first editions.
H. Rider Haggard, 1856-1925: The Haggard Papers in the Library contain some 44 letters, as well as a photograph of Haggard and additional materials documenting his career. The Library also holds approximately ninety editions of Haggard's works.
Hogarth Press: Nearly 200 works produced by and about the Hogarth Press, including early items printed and bound by the Woolfs themselves. The focus of further collecting is works produced by the press when under the direct supervision of Leonard and Virginia Woolf.
Rudyard Kipling, 1865-1936: Over 160 editions of works by Kipling, including many first and early editions, and examples of Indian, English, and American editions, among others.
Manx-language literature: Over 100 works in Manx and about the Manx language of the Isle of Man. The collection spans the 18th to 20th centuries, with a focus on the 20th century, and includes religious texts, music, periodicals, and more.
Lytton Strachey, 1880-1932: A small collection of papers includes the manuscript of his work Elizabeth and Essex and letters about that work.
Virginia Woolf, 1882-1941: Sixty editions of works by Woolf, including first and limited editions. See also the papers of Sir Leslie Stephen, Woolf's father, and the childhood diary of Dorothea Jane Stephen, Woolf's cousin.