Correspondence (1888-1953) consists primarily of the official papers generated by Millikan as chairman of the Executive Council of the California Institute of Technology which serve as a prime source for the history of the Institute. Other correspondence covers his involvement in many organizations and committees such as the National Academy of Science (1913-1952), National Research Council (1916-1926), Science Advisory Board (1933-1941), etc. as well as considerable material on the role of the Carnegie, Rockefeller, and Guggenheim foundations in the expansion of higher education in the United States in the post-World War I decades. His personal and family correspondence contains a voluminous number of letters exchanged between Millikan and his wife Greta during the frequent periods they were apart as well as Greta's correspondence with other family members and friends, providing a rich social commentary not only on the Millikan family but on contemporary events and Greta's role as a wife of a famous public figure. A small portion documents the significant role Millikan played in the mobilization of science for national defense during World War I. Family documents and memorabilia include material on their sons' early childhood, legal papers, social calenders, biographical sketches, etc. Speeches and articles cover a broad spectrum of political, social, and scientific topics. Scientific notes include lecture notes (1899-1920) which offer insight into the state of physics and physics education. Research notebooks (1897-1920) contain recorded data from his scientific experiments on electron charge measurement, bubble patent machine, photo-electric phenomena and cosmic rays. Correspondents include: Henry H. Arnold, Albert Barrows, Paul Brockett, Vannevar Bush, Harry Chandler, Karl T. Compton, Gano Dunn, Arthur H. Fleming, John A. Fleming, George E. Hale, Herbert Hoover, Frank B. Jewett, Henry M. Robinson and Theodore von Kr̀mǹ.