"Sex on Fire" is the first single released from Americanalternative rock band Kings of Leon's fourth studio albumOnly by the Night. The song gave Kings of Leon their first number-one single in Australia, Finland, Ireland and the United Kingdom, charting at the top spot on digital downloads alone in the latter country, before its physical release. In September 2009 it was Britain's second most-downloaded digital single ever. The song has sold 1.2 million copies in the United Kingdom as of November 2012. It has also gained significant popularity in the band's native United States, reaching number one on the Hot Modern Rock Tracks chart and number 56 on the Billboard Hot 100, making it their second highest charting song in their homeland on the former chart.
In an interview with Robbie, Marieke and the Doctor on Australian radio station Triple J, Nathan Followill explained that the band never intended the song to be named "Sex on Fire".
"They were totally different lyrics. Depending on whether a song starts with a melody or starts with lyrics, you know if it starts with a melody you just keep playing the melody over and over until you get it down and just throw in any lyrics that fit the verbal flow. It was actually going to be "Set Us on Fire", but one of the sound mixers in the studio walked in as we were playing and said, "Sex on Fire", huh?" And it just kind of became a running joke, and we stuck with it.".
Nathan also said that some lyrics tried were "Socks on Fire", "Snatch on Fire" and "Cocks on Fire".
The song is played in the key of E Major at a tempo of 153bpm. The vocal range is B3-G#4.
The song has received generally positive reviews. Digital Spy rated the song four stars out of five, describing it as "A truly stirring single that will be a definite highlight on their winter arena tour."The Sun also praised the song, saying it is "another of the latest album’s genuinely great and grand numbers."Planet Sound also rated the song 9/10. However, Caleb Followill originally thought the song was "terrible"; according to Spin Magazine it was almost ditched during recording. Despite giving the album a 4 out of 5, Spin thought the song was 'silly'. Music reviews blog Urbanite Youth described the song as "a rather generic rock single"  but did praise Caleb Followill for his vocal talents. This song was number 40 on Rolling Stone's list of the 100 Best Songs of 2008. This song is used for the trailer of the 2009 movie "Stay Cool".
The director of the music video for "Sex on Fire" was Sophie Muller. As of December 2014, the video has over 108 million views on YouTube. At the end of the video, Caleb opens his mouth and smoke starts coming out of his mouth. In the video, the band is seen playing in the next room at an abandoned factory. Some of the scenes in the video shows Caleb's brothers holding Caleb, who is untied to a soft mattress, Nathan washing his hair in a black water tub, Matthew explaining to Nathan and Jared about Caleb and also Matthew eating a chicken wing and Caleb looking at strange shadows while lying on a soft mattress.
In the United Kingdom, "Sex on Fire" entered at number one on the official UK Singles Chart on September 14, 2008 ― for the week ending date September 20, 2008 ― and went on to an unbroken forty two weeks on the chart, only dropping out due to the surge in sales of Michael Jackson titles immediately after his death, but after a two-week absence it was back for another thirty seven weeks, re-entering the top ten of the UK Singles Chart at number six in September 2009. Further reappearances extended its tally of weeks to ninety, making it the third most charted single of all time.
In Germany, the single debuted at number ninety seven on the German Singles Chart, and began to rise and fall in the next several weeks. In its thirty second week on the chart, the song finally reached its peak of number thirty three. As of February 2011, the song was on the chart for sixty weeks, a huge effort for a single that did not reach the top twenty. In February 2011, due to the long stay on the German Singles Chart, the single got certificated with Gold for more than 150,000 copies sold.