Amsterdam, 8 November 1955 - Institutional correspondence Willem Sandberg's letter to Josep Lluís Sert
Berlin, 1975 - Photograph View of the exhibition Kunst und Politik am Beispiel Guernica Picasso und der Spanische Bürgerkrieg
Roxbury, 22 November 1955 - Institutional correspondence Alexander Calder's letter to Willem Sandberg, dated 22 November 1955
Cambridge, Massachusetts, 8 December 1955 - Institutional correspondence Josep Lluís Sert's letter to Willem Sandberg
Amsterdam, 8 November 1955 - Institutional correspondence Willem Sandberg's letter to Alexander Calder, dated 8 November 1955
Amsterdam, 30 November 1955 - Institutional correspondence Willem Sandberg's letter to Alexander Calder, dated 30 November 1955
Amsterdam, 2 December 1955 - Personal correspondence Willem Sandberg's letter to Maurice Lefebvre-Foinet, dated 2 December 1955
Amsterdam, 3 December 1955 - Institutional correspondence Willem Sandberg's letter to Dora Maar, dated 3 December 1955
Paris, 5 December 1955 - Institutional correspondence Maurice Lefebvre-Foinet's letter to Willem Sandberg
Amsterdam, 9 December 1955 - Personal correspondence Willem Sandberg's letter to Maurice Lefebvre-Foinet, dated 9 December 1955
Zurich, 12 December 1955 - Institutional correspondence A letter from Klaus Herdeg to Willem Sandberg
Amsterdam, 16 December 1955 - Institutional correspondence Willem Sandberg's letter to Dora Maar, dated 16 December 1955
Roxbury, 12 January 1956 - Institutional correspondence Alexander Calder's letter to Willem Sandberg, dated 12 January 1956
Berlin, 1975 - Exhibition catalogue Exhibition catalogue for Kunst und Politik am Beispiel Guernica. Picasso und der Spanische Bürgerkrieg