The most extensive part of the collection is correspondence; within this series, correspondence with Karl Frederich Bonhoeffer is by far the most substantial and continuous (1927-1955). Other correspondence includes exchanges with such colleagues as E. R. Bagge, Otto Hahn, Fritz Haber, Otto Furth, and Ernest Rutherford; and documentation relating to the immigration of the Harteck family (1930s-1950s) and the Nuclear Power Project (1955-1956). The remaining series in the collection are research notes, legal papers, speeches, lectures, drafts of articles and proposals, newspaper clippings, miscellaneous, and photographs.