1. Blaauw, Adriaan (1991). ESO’s Early History. Garching, Germany: ESO. (For Oort’s role in the establishment of the ESO.)
2. — (1992). ESO Historical Archives [EHA]: Inventory per December 1992. Garching: ESO. See also the same author’s Archives of the International Astronomical Union: Inventory for the Years 1919–1970. Paris: IAU, 1999. (For archival material.)
3. — (1993). “Jan Hendrik Oort” (in Dutch). Zenit 20: 196–210.
4. — (1994). History of the IAU. Dordrecht: Kluwer Academic Publishers. (For Oort’s role in IAU.)
5. Blaauw, Adriaan and Maarten Schmidt (1993). “Jan Hendrik Oort (1900–1992).” Publications of the Astronomical Society of the Pacific 105: 681–685.