[1]Goethe-Institut USA, about Helen and Kurt Wolff, retrieved July 31, 2009
immigrantentrepreneurship.org
Detjen, Marion. "Kurt and Helen Wolff." In Immigrant Entrepreneurship: German-American Business Biographies, 1720 to the Present, vol. 5, edited by R. Daniel Wadhwani. German Historical Institute. Last modified June 19, 2012.