Correspondence, published and unpublished writings, research materials, teaching records, financial and legal records, family papers, biographical material, memorabilia, and photographs. Of particular note are letters from her grandfather, Hiram Hadley, describing his life in New Mexico and his work as an educator, 1900-1922; letters reflecting Allen's experiences as a student at Vassar College, 1912-1916, and Clark University, where she worked with A.G. Webster, 1916-1922, and her post-graduate studies, particularly with W.F.G. Swann at Yale University and the Bartol Research Foundation, 1926-1930; letters discussing her work as a physics teacher, primarily at Mount Holyoke College (1918-1959), where her colleagues included Roswell G. Ham, Elizabeth R. Laird, Rogers D. Rusk, Frederick A. Saunders; and correspondence with Erwin J. Saxl concerning their collaborative research, 1963-1981.

Also includes materials relating to her childhood in Boston and her social life, reading, health, and relationship with her parents, C. Frank and Caroline H. Allen; papers of her father, a railroad engineer and professor, 1865-1950; and letters from her sister, Margaret Allen Anderson, discussing family news and her studies at the New England Conservatory of Music.