Chiefly correspondence (1917-1960) between Leffingwell and colleagues in banking and the legal profession, and with important American and British government officials on contemporary economic and political events. Following his service in the Department of the Treasury (1917) where he helped to float the Liberty Loan, Leffingwell continued to correspond with his colleagues, S. Parker Gilbert and Albert Rathbone, as well as Carter Glass, Secretary of the Treasury (1918-1920). As a partner in the firm of J.P. Morgan from 1923 on, he received reports on economic conditions from officers of the firm in London, Paris, and Mexico. There is also a voluminous correspondence (1935-1948) with Thomas W. Lamont, his chief at the bank. He was asked for advice by every president from Woodrow Wilson to Dwight D. Eisenhower, with the exception of Coolidge. Among these letters, his correspondence with Franklin Delano Roosevelt is the most extensive. He was also consulted by eight secretaries of the Treasury and other government officials. Important journalists with whom he corresponded regularly are Walter Layton, editor of the British Economist, Walter Lippmann, and Morris Ernst. The papers also contain memoranda and speeches (1919-1958), photographs, and memorabilia.