APA (7th ed.) Citation

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

Chicago Style (17th ed.) Citation

Drucker, Peter F. Management Challenges for the 21st Century. New York: Harper Business, 1999.

MLA (8th ed.) Citation

Drucker, Peter F. Management Challenges for the 21st Century. Harper Business, 1999.