Anna Masterton Buchan (24 March 1877 – 24 November 1948) was a Scottish novelist who wrote under the pen name O. Douglas. Most of her novels were written and set between the wars and portrayed small town or village life in southern Scotland, reflecting her own life. Her first novel Olivia in India was published in 1912 by Hodder & Stoughton. Unforgettable, Unforgotten (1945) is a memoir of her brother John and of the Buchan family, while Farewell to Priorsford is her autobiography, published posthumously in 1950.