APA (7th ed.) Citation

Black, C. E., & Helmreich, E. C. (1966). Twentieth century Europe: A history (3rd ed.). Knorf.

Chicago Style (17th ed.) Citation

Black, C. E., and E. C. Helmreich. Twentieth Century Europe: A History. 3rd ed. New York: Knorf, 1966.

MLA (9th ed.) Citation

Black, C. E., and E. C. Helmreich. Twentieth Century Europe: A History. 3rd ed. Knorf, 1966.