A collection of letters written to Zimmermann. Most of the letters relate to a group of German artists called "Der Blaue Reiter" ("The Blue Rider"). Zimmermann assisted in the planning for the exhibition of the group, held at the Curt Valentin Gallery, December 7, 1954-January 8, 1955, and much of the correspondence relates to the exhibition. Included are letters from Albert Bloch, David Burliuk, Mrs. Nina Kandinsky, Paul Klee, and Gabriele Münter. Also, important files of correspondence from John B. Flamagan and George Grosz.