The "Lost Generation" was the generation that came of age during World War I. The term was popularized by Ernest Hemingway, who used it as one of two contrasting epigraphs for his novel, The Sun Also Rises. In that volume Hemingway credits the phrase to Gertrude Stein, who was then his mentor and patron. This generation included distinguished artists such as F. Scott Fitzgerald, T. S. Eliot, John Dos Passos, Waldo Peirce, Isadora Duncan, Abraham Walkowitz, Alan Seeger, Franz Kafka, Erich Maria Remarque and the composers Sergei Prokofiev, Paul Hindemith, George Gershwin, and Aaron Copland.
In A Moveable Feast, published after Hemingway's and Stein's deaths, Hemingway claims that Stein heard the phrase from a garage owner who serviced Stein's car. When a young mechanic failed to repair the car quickly enough, the garage owner shouted at the boy, "You are all a "génération perdue.":29 Stein, in telling Hemingway the story, added, "That is what you are. That's what you all are ... all of you young people who served in the war. You are a lost generation.":29 
'Lost means not vanished but disoriented, wandering, directionless — a recognition that there was great confusion and aimlessness among the war's survivors in the early post-war years.'
The 1926 publication of Ernest Hemingway's The Sun Also Rises popularized the term, as Hemingway used it as an epigraph. The novel serves to epitomize the post-war expatriate generation.:302 However, Hemingway himself later wrote to his editor Max Perkins that the "point of the book" was not so much about a generation being lost, but that "the earth abideth forever"; he believed the characters in The Sun Also Rises may have been "battered" but were not lost.:82
In his memoir A Moveable Feast, published after his death, he writes "I tried to balance Miss Stein's quotation from the garage owner with one from Ecclesiastes." A few lines later, recalling the risks and losses of the war, he adds: "I thought of Miss Stein and Sherwood Anderson and egotism and mental laziness versus discipline and I thought 'who is calling who a lost generation?'"
Variously, the term is used for the period from the end of World War I to the beginning of the Great Depression, though in the United States it is used for the generation of young people who came of age during and shortly after World War I, alternatively known as the World War I generation. Authors William Strauss and Neil Howe, well known for their generational theory, define the Lost Generation as the cohorts born from 1883 to 1900, who came of age during World War I and the Roaring Twenties. In Europe, they are mostly known as the "Generation of 1914," for the year World War I began. In France, the country in which many expatriates settled, they were sometimes called the Génération au Feu, the "Generation in Flames."
In Britain the term was originally used for those who died in the war, and often implicitly referred to upper-class casualties who were perceived to have died disproportionately, robbing the country of a future elite. Many felt "that 'the flower of youth' and the 'best of the nation' had been destroyed," for example such notable casualties as the poets Isaac Rosenberg, Rupert Brooke, Edward Thomas and Wilfred Owen, composer George Butterworth and physicist Henry Moseley.
- Lapsansky-Werner, Emma J. United States History: Modern America. Boston, MA: Pearson Learning Solutions, 2011. Print. Page 238
- Hemingway, Ernest (1996). A Movable Feast. New York: Scribner. ISBN 0-684-82499-X.
- Mellow, James R. (1991). Charmed Circle: Gertrude Stein and Company, p,273. New York: Houghton Mifflin. ISBN 0-395-47982-7.
- Hynes, Samuel (1990). A War Imagined: The First World War and English Culture. London: Bodley Head. p. 386. ISBN 0 370 30451 9.
- Mellow, James R. (1992). Hemingway: A Life Without Consequences. New York: Houghton Mifflin. ISBN 0-395-37777-3.
- Baker, Carlos (1972). Hemingway, the writer as artist. Princeton, N.J: Princeton University Press. ISBN 0-691-01305-5.
- Howe, Neil; Strauss, William (1991). Generations: The History of Americas Future. 1584 to 2069. New York: William Morrow and Company. pp. 247–260. ISBN 0-688-11912-3.
- Wohl, Robert (1979). The generation of 1914. Cambridge: Harvard University Press. ISBN 978-0-674-34466-2.
- "The Lost Generation: the myth and the reality". Aftermath – when the boys came home. Retrieved 6 November 2009.
- Winter, J. M. (November 1977). "Britain's 'Lost Generation' of the First World War". Population Studies 31 (3): 449–466. doi:10.2307/2173368.
- "What was the 'lost generation'?". Schools Online World War One. BBC. Retrieved 22 March 2012.
- Meyers, Jeffrey (1985). Hemingway: A Biography. London: Macmillan. ISBN 0-333-42126-4.
- Fitch, Noel Riley (1985). Sylvia Beach and the Lost Generation: A History of Literary Paris in the Twenties and Thirties. Norton. ISBN 0-393-30231-8.