"You're My Number One" is a song by S Club 7, released as the fourth and final single from the band's debut album, S Club on 13 December 1999. In the UK, the single was released as a double A-side with "Two in a Million", peaking at #2 on the UK singles chart. It was the first S Club 7 single to be released as a double A-side, later followed by "Say Goodbye" and "Love Ain't Gonna Wait for You" in 2003. "You're My Number One" is described as a fun up-tempo retro number.

"You're My Number One" is an upbeat, retro-styled song about a person questioning what love is to them. They feel that if love is what they are feeling, then they have to tell the person they like that they're their "number one", in that nobody else is right for them. The Miami 7 version of the song is different from the album version, as it contains a heavier drum track, features multilayered vocals from Jo in the chorus and takes on a more modern style. The Miami 7 version of the song was not actually the version heard on Miami 7, as it and the album version contain a different intro and take on different approaches than the version heard on Miami 7.

The single contains an exclusive B-side, "Down at Club S", which was performed during episode three of Miami 7, "The Blue Chevy". It is very much in a similar style to "You're My Number One", and was co-written by Simon Franglen and Angela Lupino, who also wrote "Gonna Change the World" for the group. The single also includes an alternate version of "Two in a Million" known as the 2000 version.

Like "Two in a Million", the music video for the song was shot in New York. Throughout, S Club 7 are performing a dance routine in front of a white background. Halfway through the video, the group partake in a foam fight. Towards the end, the band are joined by many more dancers who perform the same hand jive-esque routine until the end of the music video. In an interview, McIntosh recalls that each member was brought a selection of outfits to choose from to wear in the video, but he was only brought one outfit to wear, which he hated. The video has gained over one million views on YouTube as of 11 September 2014.

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