"I Kissed a Girl" is the debut single by American singer Katy Perry for her second studio album, One of the Boys. It was released on April 28, 2008, by Capitol Records as the lead single from the record. Perry co-wrote the song with Max Martin, Cathy Dennis, and its producer Dr. Luke, with additional production from Benny Blanco. "I Kissed a Girl" is a pop-rock, electropop, and disco song with elements of new wave. Perry stated its lyrics are "about the magical beauty of a woman." The song sparked controversy for its handling of homosexual themes, but in retrospect has been viewed as the beginning of LGBT awareness in pop music.

The song topped the US Billboard Hot 100 chart for seven consecutive weeks, becoming the 1,000th number-one song of the rock era. The single has sold 4.8 million digital copies in the US alone. "I Kissed a Girl" is one of eight songs by Perry to sell over 4 million digital copies in the US, the others being "Hot n Cold", "California Gurls", "Teenage Dream", "Firework", "E.T.", "Dark Horse" and "Roar". A huge hit throughout the Anglosphere, it also topped the charts in Australia, Austria, Belgium, Canada, the Czech Republic, Denmark, France, Germany, Hungary, Ireland, Italy, the Netherlands, New Zealand, Norway, Scotland, Sweden, Switzerland, and the United Kingdom. The song has been certified multi-platinum in Australia, Canada, Denmark, and the US.

The accompanying music video for the song was released on May 16, 2008. The video, directed by Kinga Burza, features Perry in a setting inspired by burlesque and Moulin Rouge styles. It features appearances from Perry's friends, including actress Shannon Woodward and singer Kesha. The song is recognized as the 10th best-selling single in the 21st century. "I Kissed a Girl" was performed and a nominee at the 51st Grammy Awards. It was also nominated for Favorite Song at the 2009 Kids' Choice Awards. The song has been performed on all of her tours. It was also included in Perry's performance in Super Bowl XLIX's Pepsi Halftime Show in 2015.