APA

Covey S. R., . (1992). Principle-centered leadership. New York: Simon & Schuster.

Chicago

Covey Stephen R, . 1992. Principle-centered leadership. New York: Simon & Schuster.

Harvard

Covey S. R., . (1992). Principle-centered leadership. New York: Simon & Schuster.

MLA

Covey Stephen R, . Principle-centered leadership. New York: Simon & Schuster. 1992.