Cleveland, 25 May 1939 - Institutional correspondence William Mathewson Milliken's letter to Sidney Janis
1940 - Internal museum documents Circulating exhibition contract for Picasso: Forty Years of His Art (second edition), between the Museum of Modern Art, New York, and the Cleveland Museum of Art
Ellen C. Oppler (ed.), <em>Picasso’s Guernica</em>, New York and London: W. W. Norton & Company, 1988, 236–238 - Essay “How Effective Is Social Protest Art? (Vietnam)”
Siracusa, New York, 15 July 1979 - Institutional correspondence Ellen Oppler's letter to Luisa Kreisberg