"God Only Knows" is a song written by Brian Wilson and Tony Asher for American rock band the Beach Boys, released in May 1966 as the eighth track on the group's album Pet Sounds. Two months later, it was released as the B-side of "Wouldn't It Be Nice" in the United States. In other countries, "God Only Knows" was the single's A-side, peaking at number 2 on the UK Singles Chart. According to historian John Robert Greene, "God Only Knows" led to the reinvention of the popular love song.

The song names God in its title and lyrics, unusual for a pop single of its time, as Asher recalled: "Unless you were Kate Smith and you were singing 'God Bless America', no one [in 1966] thought you could say 'God' in a song." The sentiments expressed in its lyric were not specific to any God, and could be addressed to any higher force, being a song about moving forward after loss. Wilson explained that his and Asher's intention was to create the feeling of "being blind but in being blind, you can see more".

Sung by his younger brother Carl Wilson, the Beach Boys' recording was produced and arranged by Brian using an unorthodox selection of instruments, including French horn, accordions, sleigh bell, harpsichord, and a quartet of violas and cellos heard throughout the piece in counterpoint. The musical structure has been variously cited for its harmonic complexity, inspiring tension through its disuse of authentic cadences and a definite key signature. Its closing section features perpetual rounds, a device that was not normally heard in popular music of the era.

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