"It's Not Unusual" is a song written by Les Reed and Gordon Mills, first recorded by a then-unknown Tom Jones, after having first been offered to Sandie Shaw. Jones recorded what was intended to be a demo for Shaw, but when she heard it she was so impressed with Jones's delivery that she declined the song and recommended that Jones release it himself. The record was the second Decca single Jones released, reaching number one in the UK Singles Chart in 1965. It was also the first hit for Jones in the US, peaking at No. 10 in May of that year. The single was released in the US on the Parrot label and also reached number 3 on Billboard's easy listening chart. The BBC initially refused to play the song because of Jones’s sexy image, but it was played by UK pirate radio. Jones performed the song several times on The Ed Sullivan Show in the US, first on 2 May 1965, then again on 13 June 1965. He sang the song again on the show when he returned on 21 April 1968.

Jones later used this song as the theme for his late 1960s–early 1970s television musical variety series This Is Tom Jones. It has since become his signature song.

In the sitcom The Fresh Prince of Bel-Air, on several occasions Carlton Banks lip-synchs to "It's Not Unusual" with comedic choreography. Tom Jones also guest-starred on the show a few times.

The first studio version of the song was subsequently released in 1995 as part of the compilation album The Legendary Tom Jones - 30th Anniversary Album.

The song's musical arranger was Les Reed. Although the guitar has been cited as having been provided by Jimmy Page of Led Zeppelin, Reed has stated that the only guitarist was Joe Moretti, who is known for his playing on "Shakin' All Over" and "Brand New Cadillac". Page does list the session in his online discography, however. Drums were played by Scottish percussionist Andy White, who had previously drummed for The Beatles. or possibly by or Ronnie Verrell, although a claim has also been made by Alan Grahame.

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