APA (7th ed.) Citation

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

Chicago Style (17th ed.) Citation

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

MLA (8th ed.) Citation

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