Amsterdam, 16 November 1953 - Institutional correspondence Willem Sandberg's letter to Pablo Picasso, dated 16 November 1953
Paris, 29 September 1955 - Institutional correspondence Daniel-Henry Kahnweiler's letter to Willem Sandberg, dated 29 September 1955
Amsterdam, 8 November 1955 - Institutional correspondence Willem Sandberg's letter to Josep Lluís Sert
Stockholm, 23 October 1956 - Institutional correspondence Ernesto de Zulueta's letter to Alberto Martín-Artajo Álvarez
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, 5 May 1953 - Institutional correspondence Willem Sandberg's letter to Eugenio Reale, dated 5 May 1953
Milan, 4 August 1953 - Institutional correspondence A letter from Fernanda Wittgens to Willem Sandberg, dated 4 August 1953
Milan, 12 August 1953 - Institutional correspondence Fernanda Wittgens' letter to Willem Sandberg, dated 12 August 1953
Amsterdam, 18 August 1953 - Institutional correspondence Willem Sandberg's letter to Eugenio Reale, dated 18 August 1953
Amsterdam, 11 September 1953 - Institutional correspondence Willem Sandberg's letter to Fernanda Wittgens
Milan, 7 October 1953 - Institutional correspondence A letter from Fernanda Wittgens to Willem Sandberg, dated 7 October 1953