APA (7th ed.) Citation

Drucker, P. F. (1999). Management challenges for the 21st century. Harper Collins Publishers.

Chicago Style (17th ed.) Citation

Drucker, Peter Ferdinand. Management Challenges for the 21st Century. New York: Harper Collins Publishers, 1999.

MLA (8th ed.) Citation

Drucker, Peter Ferdinand. Management Challenges for the 21st Century. Harper Collins Publishers, 1999.