The Mildred Allen Papers contain correspondence, published and unpublished writings, research materials, course records, financial and legal records, family papers, biographical material, memorabilia, and photographs. The correspondence represents both her personal relationships and her professional career. Of particular note are letters from her grandfather, Hiram Hadley, written between 1900-1922, describing his life in New Mexico, family news, and his work as a teacher. Also of interest are the letters written to her mother Caroline H. Allen and those from her sister, Margaret Allen Anderson, discussing family news and her studies at the New England Conservatory of Music. Many of the correspondence focus on her accomplished academic career and research, beginning with her experiences as a student at Vassar College, 1912-1916; followed by her graduate work at Clark University where she worked with renowned physicist A.G. Webster, 1916-1922; and her post-graduate studies at Yale University with physics professor W.F.G. Swann and later work under his direction with the Bartol Research Foundation, University of Delaware, 1926-1930. Further correspondence describes her teaching experiences at various institutions, including Mount Holyoke College, where her colleagues included Roswell Gray Ham, Elizabeth R. Laird, Roger D. Rusk, and Frederick A. Saunders. Finally, there are letters between Allen and Erwin J. Saxl concerning their collaborative research on torsion pendulums, 1963-1981. The research materials consist of lab reports including notes, graphs, and data measurement spanning from her graduate work to later notebooks of study on various effects on torsion pendulums. The course records primarily consist of physics exams ranging from introductory courses to advanced studies given at Mount Holyoke. The collection also includes materials relating to her childhood in Boston, her social life, readings, health and relationship with her parents. Also includes papers of her father's, C. Frank Allen, a railroad engineer and professor, 1865-1950. These papers primarily consist of professional correspondence between 1883-1955 and documents regarding the publication of his books.