Leslie Poles Hartley (30 December 1895 – 13 December 1972) was a British writer, known for novels and short stories. His best known work is The Go-Between (1953), which was made into a 1970 film, directed by Joseph Losey with a star cast, in an adaptation by Harold Pinter. The book's opening sentence, "The past is a foreign country: they do things differently there", has become almost proverbial.

Hartley was born in Whittlesey, Cambridgeshire, where he lived with his parents, Bessie and Harry and his two sisters, Enid and Annie Norah. He then moved to an estate near Peterborough with his family. He was educated in Cliftonville, Thanet, then briefly at Clifton College, where he first met Clifford Henry Benn Kitchin, and at Harrow School.

In 1915 he went up to Balliol College, Oxford, to read modern history. There he befriended Aldous Huxley. In 1916 he joined the British Army. He was commissioned as an officer but for health reasons never left the United Kingdom. Invalided out, he returned to Oxford in 1919, where he gathered a number of literary friends, including Lord David Cecil.

His work was published in Oxford Poetry in 1920 and 1922. He edited Oxford Outlook, with Gerald Howard and A. B. B. Valentine in 1920, and in 1921 with Basil Murray and M. C. Hollis also. At this time he was introduced by Huxley to Lady Ottoline Morrell. Kitchin, who was at Oxford also, introduced him to the Asquiths; Cynthia Asquith became a lifelong friend. Despite being named after Leslie Stephen, Hartley always belonged to the Asquith milieu, and was rebuffed by the Bloomsbury group.

Success came with having his first writing published and becoming a reviewer after his Oxford degree. Though this gave him rapid social elevation his life remained very strained, and in 1922 he suffered a nervous breakdown. Soon afterwards he started spending much time in Venice; he continued to do so for many years.

Until the success of The Go-Between he gained little recognition. He was, however, awarded the 1947 James Tait Black Memorial Prize for Eustace and Hilda and in 1956 he was awarded the CBE.

There is a critical analysis of Hartley's ghost stories in Jack Sullivan's book Elegant Nightmares: The English Ghost Story From Le Fanu to Blackwood (1978). A critical essay on Hartley's ghost stories appears in S. T. Joshi's book The Evolution of the Weird Tale (2004).