"Happy Days" is a song written by Norman Gimbel and Charles Fox. It is the theme song of Happy Days. It can be heard during the TV show's opening and closing credits as it runs in perpetual rerun syndication.

The song was first recorded in 1974 by Jim Haas with a group of other session singers for the first two seasons. These versions of the song were used only during the closing credits of Seasons 1 and 2, with an updated version of "Rock Around the Clock" by Bill Haley and His Comets used as the opening theme. The song was re-recorded in 1975 with different lyrics for both the opening and closing credits for Seasons 3 through 10. Pratt & McClain released the song as a single in 1976 from their album Pratt & McClain Featuring Happy Days. Bobby Arvon recorded an updated version the song in 1983 for the opening and closing credits of Season 11, with the same lyrics as the version used for seasons 3-10.

Pratt & McClain's album version of the song, recorded in 1976, peaked at No. 5 on the Billboard Hot 100, No. 7 on the Easy Listening chart and No. 31 on the UK Singles Chart.

Australian band Silver Studs also recorded a version of the theme for their debut album. It became their biggest hit single in Australia, reaching #4 in June, 1976.

In 2014, a re-recorded version of the song was used in commercials for Target.

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