Correspondence, speeches, lectures, literary manuscripts including books and plays, articles, subject file, research material, newspaper clippings, scrapbooks, printed matter, memorabilia, photographs, and other papers pertaining chiefly to Middleton's career as a playwright, author, and copyright specialist at the U.S. Dept. of Justice. Subjects include the protection of foreign and domestic playwrights' monetary and literary rights in the publication and production of their works, Robert M. La Follette's 1924 presidential campaign, Middleton's marriage to Fola La Follette, and his relationships with members of the theatrical, literary, and political communities. Includes material pertaining to Middleton's collaborations with David Belasco and Guy Bolton and to his association with the Dramatists Guild, Dutch Treat Club, and the Players Club. Includes drafts of his autobiography, These Things Are Mine (1947), and correspondence of Fola La Follette and other La Follette and Middleton family members.

Other correspondents include J.M. Barrie, Louis Dembitz Brandeis, Cecil B. DeMille, John Dos Passos, Eleanora Duse, Anatole France, Felix Frankfurter, Hamlin Garland, Moss Hart, George S. Kaufman, Sinclair Lewis, David Eli Lilienthal, Percy MacKaye, Don Marquis, John Masefield, Edgar Lee Masters, H.L. Mencken, Gerald P. Nye, Clifford Odets, Eugene O'Neill, Richard Rodgers, Eleanor Roosevelt, Franklin D. Roosevelt, Bernard Shaw, Lincoln Steffens, Booth Tarkington, P.G. Wodehouse, and Peggy Wood.