The Correspondence series contains Widenmann's professional correspondence with bankers, businessmen, government officials, and academics. The majority of the letters are in response to Widenmann's requests for copies of articles or speeches, often with the requested item and sometimes with Widenmann's comments on the item. The series also includes correspondence between Widenmann and United States government officials regarding his views of financial policies, Widenmann writing colleagues about the state of the stock market and United States financial conditions more generally, correspondence in relation to his involvement with professional organizations and conferences, and invitations to events.