"Underneath It All" is a song written by Gwen Stefani and Dave Stewart for No Doubt's fourth album Rock Steady (2001). The song features reggae production from Mad Lion and guest vocals from deejay Lady Saw. It received mixed reviews from pop music critics.

"Underneath It All" was released as the album's third single in mid-2002. It became No Doubt's highest-charting American single but was less successful elsewhere. The song won a Grammy Award for Best Pop Performance by a Duo or Group with Vocal at the 46th Grammy Awards. The song was featured in the film 50 First Dates (2004).

The song was originally written by Stefani and Stewart during Stefani's visit to boyfriend Gavin Rossdale in London. The two used backward string samples to write the song in only ten minutes. The song describes Stefani's relationship with Rossdale, and the line "You're really lovely underneath it all" comes from a journal entry that Stefani made after spending a day in the park with Rossdale. Guitarist Tom Dumont commented that Stewart's experience helped them keep the song simple because he "would have way overthought those chord changes." When the band was working on the album in Jamaica, producers Sly & Robbie called dancehall artist Lady Saw to have her contribute a guest toast. After listening to the track, Lady Saw wrote and recorded her part on the spot.

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