Girlfriend, a song by Canadian singer Avril Lavigne, is the lead single from her third album, The Best Damn Thing (2007). It was produced by Lukasz "Dr. Luke" Gottwald. Girlfriend became Lavigne's biggest hit in the United States, where it reached number one on the U.S. Billboard Hot 100. It topped the chart in Australia for 6 weeks, and reached number two in the United Kingdom. A remix featuring rapper Lil Mama was released in June 2007.
The song involves Lavigne proclaiming a crush on a boy currently with his girlfriend and features the typical 80' pop-punk influence and power pop of her earlier songs. Lavigne said on the DVD side of the deluxe edition of The Best Damn Thing that in the bridge when the listener hears hand clapping, the accompanying giggling was created by Lavigne and Gottwald, despite it sounding like a girl. The Japanese version of this song replaces the word motherfucking with the phrase "one and only" in the line "Hell yeah, I'm the motherfucking Princess". Girlfriend is in the video game Burnout Dominator in English, Japanese, Spanish, and Chinese. It also appears in Burnout Paradise but this time only in English. This song is recorded in 7 languages other than English. It is the theme song of Japanese talk show Cartoon KAT-TUN - on which Lavigne appeared on May 2, 2007 - as well as being the insert song for popular Japanese manga based drama Hanazakari no Kimitachi e. It is featured in the theatrical trailer for the 2007 live-action Bratz film, and in a trailer for the film I Now Pronounce You Chuck and Larry, and also for Bring It On: In It to Win It. Lavigne performed the song on The Tonight Show with Jay Leno on June 15, 2007.
Girlfriend was premiered on Edmonton radio station The Bounce 91.7 before the official date it was supposed to be aired; the two DJs who played it were taken off the air shortly after. The single appeared and was available for download on the U.S. iTunes Store on February 23, but was subsequently removed the following day. It was made available again on February 27.
Because of digital download sales in excess of 122,000, the song debuted at number five on the U.S. Billboard Hot 100 chart, the highest debut of her career. Afterwards it became Lavigne's first song to reach number one on the Hot 100, in the issue dated May 5, 2007; her previous highest peak on the chart was with 2002's Complicated, which reached number two. It remained in the top ten for eighteen weeks, and has since been downloaded over 2.6 million times.
Girlfriend debuted on the Australian ARIA Singles Chart at number three. The following week it reached number-one, and it remained at the top for six non-consecutive weeks, equaling Lavigne's previous number-one single on the ARIA Charts, Complicated. After three weeks on the charts, it was certified gold by ARIA, then platinum after seven weeks for sales in excess of 70,000 copies. It was then certified double platinum, sales in excess of 140,000.
On the UK Singles Chart, Girlfriend peaked at number two, surpassing Complicated as Lavigne's highest peaking single on the chart. The song ended 2007 as the years 20th biggest-selling single in the UK.
In Latin America, the single peaked at number three. In Mexico, the song became the second top ten single in English of 2007 when it climbed to number eight; it later peaked at number two. It won the Award for Canción del Año (Song Of The Year) in Los Premios MTV Latinoamérica 2007 (The Latin American MTV Awards) and was nominated for "Monster Single" in the MTV Video Music Awards 2007. It won Addictive Track for the MTV Europe Music Awards.