APA (7th ed.) Citation

Verdi, G., Werfel, F., & Stefan, P. (1973). Verdi, the man in his letters. Vienna House.

Chicago Style (17th ed.) Citation

Verdi, Giuseppe, Franz Werfel, and Paul Stefan. Verdi, the Man in His Letters. New York: Vienna House, 1973.

MLA (9th ed.) Citation

Verdi, Giuseppe, et al. Verdi, the Man in His Letters. Vienna House, 1973.