The Little Girl I Once Knew is a song written by Brian Wilson for the American pop band The Beach Boys. It was released in November 1965 as a single 45 rpm, backed by "There's No Other (Like My Baby)", and reached #15 on the Cashbox chart, #20 on Billboard. The last new original song the group produced before the album Pet Sounds, it was not included on any regular Beach Boys album, but has since been collected on several anthologies and as a bonus track on reissues of Summer Days (and Summer Nights!!).

The song is notable for innovative use of two dramatic periods of near-silence lasting several seconds each. Although one of the Beach Boys' most exuberant songs, it was poorly received by radio stations preferring to avoid dead air time, which may account for its relatively low chart rating among their other singles of the period, including "California Girls" and "Barbara Ann". It is still rarely heard on oldies radio.

Capitol Records' rushed release of Barbara Ann in December ruined any chance LGIOK had of continuing up the charts. Just after its release, John Lennon gave it a favorable review; another what-if for the Beach Boys.