Rapone, Anita. The Guardian Life Insurance Company, 1860–1920: A History of a German-American Experience. . New York: New York University Press, 1987.
Wright, Robert E. and George David Smith. Mutually Beneficial: The Guardian and Life Insurance in America. . New York: New York University Press, 2004.
Archival Collections
Erinnerungen aus dem Jahre 1848New York: [n.p], 1898
Corporate ArchivesGuardian Life Insurance Company, New York, N.Y.
