Correspondence, reprints, proposals, monographs, research data, clippings, and notes from lectures, conferences, travel, and courses. Also included are materials relating to his work with many government and professional organizations, e.g., the Atomic Energy Commission, National Academy of Sciences, and the American Physical Society. Bulk of the collection is from after World War II. A principal correspondent is Fay Ajzenberg-Selove. Other correspondents include his father, C. C. Lauritsen, Luis Alvarez, Hans Bethe, Niels and Aage Bohr, and William A. Fowler.