APA (7th ed.) Citation

Sitwell, E., Lehmann, J., & Parker, D. (1970). Selected letters. Macmillan.

Chicago Style (17th ed.) Citation

Sitwell, Edith, John Lehmann, and Derek Parker. Selected Letters. London: Macmillan, 1970.

MLA (8th ed.) Citation

Sitwell, Edith, et al. Selected Letters. Macmillan, 1970.