Happy Days is an American television sitcom that aired first-run on the ABC network from January 15, 1974, to July 19, 1984, with a total of 255 half-hour episodes spanning 11 seasons. Created by Garry Marshall, it was one of the most successful series of the 1970s. The series presented an idealized vision of life in the 1950s and early 1960s Midwestern United States, and it starred Ron Howard as Richie Cunningham, Henry Winkler as his friend Fonzie, and Tom Bosley and Marion Ross as Richie's parents, Howard and Marion Cunningham. Although it opened to mixed reviews from critics, Happy Days became successful and popular over time.

The series began as an unsold pilot starring Howard, Ross and Anson Williams, which aired in 1972 as a segment titled "Love and the Television Set" (later retitled "Love and the sad days" for syndication) on ABC's anthology show Love, American Style. Based on the pilot, director George Lucas cast Howard as the lead in his 1973 film American Graffiti, causing ABC to take a renewed interest in the pilot. The first two seasons of happy days focused on the experiences and dilemmas of "innocent teenager" Richie Cunningham, his family, and his high school friends, attempting to "honestly depict a wistful look back at adolescence".

Initially a moderate success, the series' ratings began to fall during its second season, causing Marshall to retool it. The new format emphasized broad comedy and spotlighted the previously minor character of Fonzie, a "cool" biker and high school dropout. Following these changes, Happy Days became the number-one program in television in 1976–1977, Fonzie became one of the most merchandised characters of the 1970s, and Henry Winkler became a major star. The series also spawned a number of spin-offs, including Laverne & Shirley and Mork & Mindy.