is a novel by Arthur Koestler, first published in 1940. His best known work, it is the tale of Rubashov, an Old Bolshevik who is arrested, imprisoned, and tried for treason against the government that he had helped to create. It is set in 1938 during the Stalinist Great Purge and Moscow show trials as Stalin eliminated potential threats to his dictatorship. The novel does not name either Russia or the USSR, but the characters have Russian names. Joseph Stalin is represented by "Number One".

Darkness at Noon was written in German while Koestler was living in Paris. His companion, the sculptor Daphne Hardy, translated it into English during early 1940 while she was living in Paris with him. For decades the German text was thought to have been lost during the escape of Koestler and Hardy from Paris in May 1940, just before the German occupation of France. However, in August 2015 a copy of the orignial manuscript that had been sent to a Swiss publisher was identified in a Zurich library by a doctoral candidate of the University of Kassel.

(5 September 1905 – 1 March 1983) was a Hungarian-British author and journalist. Koestler was born in Budapest and, apart from his early school years, was educated in Austria. In 1931 Koestler joined the Communist Party of Germany until, disillusioned by Stalinism, he resigned in 1938. In 1940 he emigrated to Britain and published his novel Darkness at Noon, an anti-totalitarian work that gained him international fame. Koestler embraced many causes, Zionism, Communism, anti-Communism, voluntary euthanasia and the abolition of capital punishment among them. In 1979 he was diagnosed with terminal leukaemia. In 1983 he and his wife killed themselves at their home in London.