Kay Boyle (February 19, 1902 – December 27, 1992) was an American novelist, short story writer, educator, and political activist. Boyle is best known for her fiction, which often explored the intersections of personal and political themes. Her work contributed significantly to modernist literature, and she was an active participant in the expatriate literary scene in Paris during the 1920s. She was a Guggenheim Fellow and O. Henry Award winner.

The granddaughter of a publisher, Boyle was born in St. Paul, Minnesota, and grew up in several cities but principally in Cincinnati, Ohio. She had one sibling, an elder sister, Joan (1900–1993), later Mrs. Detweiler. Their father, Howard Peterson Boyle, was a lawyer, and their mother was Katherine (Evans) Boyle, a literary and social activist who believed the wealthy had an obligation to help the financially less fortunate. In later years, Kay Boyle championed integration and civil rights. She advocated banning nuclear weapons, and American withdrawal from the Vietnam War.

Boyle was educated at the exclusive Shipley School in Bryn Mawr, Pennsylvania, then studied architecture at the Ohio Mechanics Institute in Cincinnati. Interested in the arts, she studied violin at the Cincinnati Conservatory of Music before settling in New York City in 1922 where she found work as a writer/editor with a small magazine.

That same year, she met and married a French exchange student, Richard Brault, and they moved to France in 1923. This resulted in her staying in Europe for the better part of the next twenty years. Separated from her husband, she formed a relationship with magazine editor Ernest Walsh, with whom she had a daughter, Sharon, named for the Rose of Sharon, in March 1927, five months after Walsh's death from tuberculosis in October 1926.

In 1928 she met Laurence Vail, who was then married to Peggy Guggenheim. Boyle and Vail lived together between 1929 until 1932 when, following their divorces, they married. With Vail, she had three more children - daughters Apple-Joan in 1929, Kathe in 1934, and Clover in 1939. During her years in France, Boyle was associated with several innovative literary magazines and made friends with many of the writers and artists living in Paris around Montparnasse. Among her friends were Harry and Caresse Crosby who owned the Black Sun Press and published her first work of fiction, a collection titled Short Stories. They became such good friends that in 1928 Harry Crosby cashed in some stock dividends to help Boyle pay for an abortion. Other friends included Eugene and Maria Jolas. Boyle also wrote for transition, one of the preeminent literary publications of the day. A poet as well as a novelist, her early writings often reflected her lifelong search for true love as well as her interest in the power relationships between men and women. Boyle's short stories won two O. Henry Awards.

In 1936, she wrote a novel, Death of a Man, an attack on the growing threat of Nazism. In 1943, following her divorce from Laurence Vail, she married Baron Joseph von Franckenstein, with whom she had two children - Faith in 1942 and Ian in 1943. After having lived in France, Austria, England, and in Germany after World War II, Boyle returned to the United States.

In the States, Boyle and her husband were victims of early 1950s McCarthyism. Her husband was dismissed by Roy Cohn from his post in the Public Affairs Division of the United States Department of State, and Boyle lost her position as foreign correspondent for The New Yorker, a post she had held for six years. She was blacklisted by most of the major magazines. During this period, her life and writing became increasingly political.

She and her husband were cleared by the United States Department of State in 1957.