APA

Drucker (Peter F), . (1999). Management Challenges For The 21 St Century. : .

Chicago

Drucker (Peter F), . 1999. Management Challenges For The 21 St Century. : .

Harvard

Drucker (Peter F), . (1999). Management Challenges For The 21 St Century. : .

MLA

Drucker (Peter F), . Management Challenges For The 21 St Century. : . 1999.