"My World Fell Down" is a song written by John Carter and Geoff Stephens, and first recorded by the English pop rock band the Ivy League, on Pye Records, in 1966 (see 1966 in music). The song was covered a year later by the American sunshine pop group Sagittarius, and managed to chart on the Billboard Hot 100. Sagittarius's version of the composition has remained highly sought after among record collectors for its close resemblance to the Pet Sounds-era Beach Boys.

The Ivy League, a Beach Boys-inspired band led by John Carter, recorded "My World Fell Down" in 1966, and scored a minor hit in the UK. In its original form, the song is reminiscent of the Turtles' hit tune "Happy Together", with a minor-key string-led verse, and baroque pop instrumental breaks. Upon hearing the band's composition, record producer Gary Usher was convinced that he could rearrange "My World Fell Down" into a major commercial success, with a duo he was then-currently producing, Chad & Jeremy. However, the two refused to record another musical artist's song, leaving Usher without a willing participant to record "My World Fell Down". Undeterred, Usher recruited Los Angeles session musicians, along with longtime friends Glen Campbell and Bruce Johnston, and innovative songwriter Curt Boettcher to record the song under the moniker, Sagittarius.

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