APA (7th ed.) Citation

Wagner, C., Skelton, G., Mack, D., & Gregor-Dellin, M. (1978). Cosima Wagner's Diaries. Collins.

Chicago Style (17th ed.) Citation

Wagner, Cosima, Geoffrey Skelton, Dietrich Mack, and Martin Gregor-Dellin. Cosima Wagner's Diaries. London: Collins, 1978.

MLA (9th ed.) Citation

Wagner, Cosima, et al. Cosima Wagner's Diaries. Collins, 1978.