Correspondence; diaries; manuscripts; lectures; reprints; financial and legal documents; testimonials; photographs; student notebooks; postcards. The collection is important primarily for its intellectual and social history. With the exception of the reprints, lectures, and college notes, there is little substantive scientific information. It is made up largely of correspondence (1872-1978) which is primarily social in content, and includes a significant quantity of family letters and history. Darrow's wide international circle of friends in both the arts and sciences reflect such events in the correspondence as the Depression, World War II, the influx of foreign scientists into the United States, the impact of the development of the atomic bomb within the physics community, the increasing participation of women in science, Presidential campaigns, and political developments in both the United States and Europe. There is a small series of professional correspondence from Darrow's office at Bell Laboratories (1955-1956) which deals mainly with his retirement and his work as Secretary of the American Physical Society. Correspondents include Raymond T. Birge, Niels Bohr, Lǒn Brillouin, Clinton Joseph Davisson, Arthur J. Dempster, Jesse W. Du Mond, Enrico Fermi, Ernest O. Lawrence, Leona Marshall, R. A. Millikan, George Mulfinger, Manuel Vallarta, John H. Van Vleck, and Ralph W. Wyckoff among many others. Testimonial letters from his retirement represent some of the most imporant names in the international scientific community. The biographical materials include family histories, wills, obituaries and some of Darrow's childhood writings. The diaries (1902-1972) contain accounts of travels, appointments and daily activities. There are copies of many of Darrow's lectures, including an annotated copy of his Lowell Lectures of 1935, manuscripts, and a complete set of reprints of his published articles. Darrow's college notes include those from his Freshman physics course with R. A. Millikan in 1908 at the University of Chicago. Random financial information includes tax forms, investment records, contracts and family estate settlement papers. Photographs include family and professional pictures. Among the correspondence are approximately 800 picture postcards (1917-1976) from the United States and around the world.