Daisy Fay Buchanan (/bjuːˈkænən/ ^ⓘ bew-KAN-ən) is a fictional character in F. Scott Fitzgerald's 1925 novel The Great Gatsby. The character is a wealthy socialite from Louisville, Kentucky who resides in the fashionable, "old money" town of East Egg on Long Island, near New York City, during the Jazz Age. She is Nick Carraway's second cousin, once removed, and the wife of polo player Tom Buchanan, with whom she has a daughter named Pammy. Before marrying Tom, Daisy had a romantic relationship with poor doughboy Jay Gatsby. Her choice between Gatsby and Tom becomes the novel's central conflict.

Fitzgerald based the character on socialite Ginevra King with whom he shared a romance from 1915 to 1917. Their relationship ended after King's father purportedly warned the writer that "poor boys shouldn't think of marrying rich girls", and a heartbroken Fitzgerald enlisted in the United States Army amid World War I. While Fitzgerald served in the army, King's father arranged her marriage to Bill Mitchell, a polo player who partly served as the model for Tom Buchanan. After King's separation from Mitchell, Fitzgerald attempted to reunite with King in 1938, but his alcoholism doomed their reunion. Scholar Maureen Corrigan states that Ginevra, far more than Fitzgerald's wife Zelda, became "the love who lodged like an irritant in Fitzgerald's imagination, producing the literary pearl that is Daisy Buchanan".

Scholars identify Daisy as personifying the cultural archetype of the flapper, young women who bobbed their hair, wore short skirts, drank alcohol and engaged in premarital sex. Despite the new societal freedoms attained by women in the 1920s, Fitzgerald's novel examines the continued limitations on their agency during this period. Although early critics viewed Daisy as a "monster of bitchery", later scholars posited that Daisy exemplifies the marginalization of women in the elite milieu that Fitzgerald depicts. The contest of wills between Tom and Gatsby reduces Daisy, described by Fitzgerald as a "golden girl", to a trophy wife whose sole existence is to augment her possessor's status, and she becomes the target of both Tom's callous domination and Gatsby's dehumanizing adoration.

The character has appeared in various media related to the novel, including stage plays, radio shows, television episodes, and films. Actress Florence Eldridge originated the role of Daisy on the stage in the 1926 Broadway adaptation of Fitzgerald's novel at the Ambassador Theatre in New York City. That same year, Lois Wilson played the role in the now lost 1926 silent film adaptation. During the subsequent decades, many actresses have played the role, including Betty Field, Phyllis Kirk, Jeanne Crain, Mia Farrow, Mira Sorvino, Carey Mulligan, and Eva Noblezada among others.

Fitzgerald based the character of Daisy Buchanan on Chicago socialite Ginevra King. While a sophomore at Princeton, the 18-year-old aspiring writer fell deeply in love with the 16-year-old King during a visit to his hometown of St. Paul, Minnesota. At the time, Ginevra was "a rich and wildly popular visitor from Chicago, who at sixteen had the social ease of a young duchess. A beauty with dark curling hair and large brown romantic eyes, she had an air of daring and innocent allure. To Fitzgerald, Ginevra King was the embodiment of a dream, and he was immediately and completely captivated."

Fitzgerald and King shared a passionate romance from 1915 to 1917, and King declared herself to be "madly in love" with him. During this time, Fitzgerald visited Ginevra at her family's estate in the upper-class enclave of Lake Forest, Illinois. As Lake Forest socially excluded Black and Jewish residents, the appearance of a middle-class Irish Catholic parvenu such as Fitzgerald in the predominantly White Anglo-Saxon Protestant milieu likely caused a stir and upset Ginevra's parents. Ginevra's imperious father, Charles Garfield King, purportedly told Fitzgerald that "poor boys shouldn't think of marrying rich girls".

After her family's intervention ended their relationship, a heartbroken Fitzgerald dropped out of Princeton and enlisted in the United States Army amid World War I. While Fitzgerald served in the army, King's father arranged her marriage to Bill Mitchell [wd], the son of his business associate John J. Mitchell. An avid polo player, Bill Mitchell became the director of Texaco, one of the most successful oil companies, and he partly served as the model for Tom Buchanan in The Great Gatsby. Ginevra informed Fitzgerald of her impending marriage via a letter that he received while in the army.

According to scholar James L. W. West, Ginevra's arranged marriage to Bill Mitchell functioned as a dynastic union between two wealthy Chicago families, and Bill's brother Clarence likewise married Ginevra's sister Marjorie. By consenting to marry the scion of her father's business partner in order to cement an alliance between two powerful Chicago families, an obedient Ginevra "made the same choice Daisy Buchanan did, accepting the safe haven of money rather than waiting for a truer love to come along."