Girlfriend EP Single • Avril Lavigne • 2007

"Girlfriend" is a song by Canadian singer-songwriter Avril Lavigne. The song was written by Lavigne and Dr. Luke; the latter is also the producer. "Girlfriend" was released as the lead single from her third studio album, The Best Damn Thing (2007) on 27 February 2007 by Columbia and RCA Records. Lyrically, the song revolves around its protagonist having a crush on someone who is in a relationship, proclaiming she should be his girlfriend. The song has been noted to have similarities to Toni Basil's 1982 single "Mickey", and The Rubinoos' 1979 single "I Wanna Be Your Boyfriend". The songwriters of "I Wanna Be Your Boyfriend" sued Lavigne and Dr. Luke for copyright infringement; the suit was later settled.

"Girlfriend" received generally positive reviews from music critics, who complimented its catchiness. The song was a worldwide success, peaking at the top spot of the charts in eight countries, including Australia, New Zealand, Canada and was Lavigne's first number-one song in the United States, reaching the top on Billboard Hot 100 and Billboard Top 40 Mainstream. It additionally charted in the top ten of most other countries. The song's accompanying music video, directed by The Malloys, sees Lavigne portraying three alter-egos, with all of them fighting over the same guy. In June 2007, the song's official remix, featuring American rapper Lil Mama, was released. Lavigne performed the song a number of times, including at the 2007 MuchMusic Video Awards, the 2007 Teen Choice Awards, and the 2008 Juno Awards.

The song's success made it a mainstay of pop music in the late 2000s. "Girlfriend" was certified multi-platinum in Australia and the United States. It was among the top-selling songs of 2007, with over 7.3 million worldwide sales. In 2008, the song became the most viewed video on YouTube, and was the first video on the site to reach 100 million views. Rolling Stone ranked the song number thirty-five on their "Top 100 Songs of 2007" list. Several versions of the song were released with the chorus sung in multiple languages. In 2010, the song was named the ninety-fourth most successful song on the Hot 100 in the 2000s decade. Allmusic highlighted the song as one of the most significant punk-pop songs of all time. The song also received several awards, including Most Addictive Track at the MTV Europe Music Awards, Song of the Year at Los Premios MTV Latinoamérica, Choice Music: Single at Teen Choice Awards, the Nickelodeon Kids' Choice Award for Favorite Song and was nominated for Single of the Year at the Juno Awards.