"Ex-Girlfriend" is a song written by Tom Dumont, Tony Kanal, and Gwen Stefani for No Doubt's fourth studio album Return of Saturn (2000). The song was released as the album's first official single in mid-2000 (see 2000 in music) and it was moderately successful, reaching the top 40 in most countries.

Gwen Stefani originally composed the song as a dirge about her relationship with Bush's lead singer Gavin Rossdale, whom she married in 2002. After listening to it, the band increased the tempo because the album already included several ballads. The line "you say you're gonna burn before you mellow" is a reference to the lyrics in the Bush song "Dead Meat": "I'm doing you in tomorrow/I'll burn before I mellow".

"Ex-Girlfriend" is a song composed in the key of E minor. It is written in common time and moves at a fast tempo of 168 beats per minute. Stefani's vocal range in the song covers nearly an octave and a half, from G₃ to C₅. It features flamenco guitar riffs and influence from new wave and hip hop.

The song's music video, which the video itself indicated was "presented" by Hype Williams, was partially based on the highly controversial anime Kite. In the video, Stefani cross-dresses to enter a men's bathroom and, upon being discovered, assaults Tony Kanal (who plays her ex-boyfriend) and several other men. When Kanal regains consciousness, he grabs Stefani and jumps out the window, and the two plummet to the ground. The storyline is cut with scenes of the band playing on a stage. No Doubt's guitarist Tom Dumont initially played the part of a police officer but was cut from the final version of the "Ex-Girlfriend" video. He enacts the role in MTV's Making the Video.

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