APA (7th ed.) Citation

Wagner, R., Flagstad, K., & Knappertsbusch, H. (1956). Kirsten Flagstad sings Wagner. London.

Chicago Style (17th ed.) Citation

Wagner, Richard, Kirsten Flagstad, and Hans Knappertsbusch. Kirsten Flagstad Sings Wagner. England: London, 1956.

MLA (9th ed.) Citation

Wagner, Richard, et al. Kirsten Flagstad Sings Wagner. London, 1956.