APA
Drucker P. F., . (1999). Management challenges for the 21st century. New York: HarperCollins Publishers.
Chicago
Drucker Peter Ferdinand, . 1999. Management challenges for the 21st century. New York: HarperCollins Publishers.
Harvard
Drucker P. F., . (1999). Management challenges for the 21st century. New York: HarperCollins Publishers.
MLA
Drucker Peter Ferdinand, . Management challenges for the 21st century. New York: HarperCollins Publishers. 1999.