Happy Days-Traditional By Estelle Bertrand Happy Days is based on an 18th century gospel hymn. Recorded in 1969, the song quickly became a hit that has since been covered by a host of international performers. The key is G major and the eighth notes are played with a zest of swing. In this version, the melody is first presented over an eighth note accompaniment (bars 1-11), before being integrated into a harmonic part with major chords.