Sidney Aaron "Paddy" Chayefsky (/ˌtʃaɪˈ(j)ɛfski/; January 29, 1923 – August 1, 1981) was an American playwright, screenwriter and novelist. He is the only person to have won three solo Academy Awards for writing both Adapted and Original screenplays.

He was one of the most renowned dramatists of the Golden Age of Television. His intimate, realistic scripts provided a naturalistic style of television drama for the 1950s, dramatizing the lives of ordinary Americans. Martin Gottfried wrote in All His Jazz that Chayefsky was "the most successful graduate of television's slice of life school of naturalism."

Following his critically acclaimed teleplays, Chayefsky became a noted playwright and novelist. As a screenwriter, he received three Academy Awards for Marty (1955), The Hospital (1971) and Network (1976). The movie Marty was based on his own television drama about two lonely people finding love. Network was a satire of the television industry and The Hospital was also satiric. Film historian David Thomson called The Hospital "years ahead of its time. … Few films capture the disaster of America's self-destructive idealism so well." His screenplay for Network is often regarded as his masterpiece, and has been hailed as "the kind of literate, darkly funny and breathtakingly prescient material that prompts many to claim it as the greatest screenplay of the 20th century."

Chayefsky's early stories were frequently influenced by the author's childhood in The Bronx. Chayefsky was part of the inaugural class of inductees into the Academy of Television Arts & Sciences' Television Hall of Fame. He received this honor three years after his death, in 1984.

Sidney Aaron Chayefsky was born in the Bronx, New York City, to Russian-Jewish immigrants Harry and Gussie (Stuchevsky) Chayefsky. Harry Chayefsky's father served for twenty-five years in the Russian army so the family was allowed to live in Moscow, while Gussie Stuchevsky lived in a village near Odessa. Harry and Gussie immigrated to the United States in 1907 and 1909 respectively.

Harry Chayefsky worked for a New Jersey milk distribution company in which he eventually took a controlling interest and renamed Dellwood Dairies. The family lived in Perth Amboy, New Jersey, and Mount Vernon, New York, moving temporarily to Bailey Avenue in the West Bronx at the time of Sidney Chayefsky's birth while a larger house in Mount Vernon was being completed. He had two older brothers, William and Winn.

As a toddler, Chayefsky showed signs of being gifted, and could "speak intelligently" at two and a half. His father suffered a financial reversal during the Wall Street Crash of 1929, and the family moved back to the Bronx. Chayefsky attended a public elementary school. As a boy, Chayefsky was noted for his verbal ability, which won him friends. He attended DeWitt Clinton High School, where he served as editor of the school's literary magazine The Magpie. He graduated from Clinton in 1939 at age 16 and attended the City College of New York, graduating with a degree in social sciences in 1943. While at City College he played for the semi-professional football team Kingsbridge Trojans. He studied languages at Fordham University during his Army service.

In 1943, two weeks before his graduation from City College, Chayefsky was drafted into the United States Army, and served in combat in Europe. While in the Army he adopted the nickname "Paddy." The nickname was given spontaneously when he was awakened at dawn for kitchen duty. Although actually Jewish, he asked to be excused to attend Mass. "Sure you do, Paddy," said the officer, and the name stuck.