"It Ain't Me" is a song by Norwegian DJ Kygo and American singer Selena Gomez. It was released by Interscope and Ultra on 17 February 2017 as the first single from Kygo's upcoming second studio album. The song was written by Kygo, Gomez, Andrew Watt, Brian Lee and Ali Tamposi. It was produced by Kygo, Watt, Ben Rice and Louis Bell. An EDM and tropical house song, "It Ain't Me" comprises an acoustic guitar line, and a build-drop arrangement in its chorus featuring pulsing piano notes, bass, synthesizers, finger-snap claps and pan flute melodies. Gomez sings the track in a husky tone, while in the chorus her vocals are reduced to recurring syllables. The lyrics are nostalgic and narrate a past relationship ruined by alcoholism and partying too often.

In addition to debuting at number one in Norway, the song attained a top five peak in Australia, Austria, Belgium, Canada, the Czech Republic, Denmark, Finland, Germany, Ireland, the Netherlands, New Zealand, Poland, Portugal, Slovakia, Sweden and Switzerland. It also reached the top 10 in France, Hungary, Italy, Spain, the United Kingdom and the United States.

The lyrics of "It Ain't Me" were written by Andrew Watt, Brian Lee and Ali Tamposi in London where the three had success writing a number of songs. With Watt previously working with Kygo, the DJ's manager Myles Shear contacted Watt for a session with Kygo which Watt also facilitated for Lee and Tamposi. During their session for "It Ain't Me", they initially found the track very poor, but were trying to salvage it. Kygo and Shear suggested that they continue working on the song. After Kygo and Shear had left, Tamposi told Watt and Lee to play guitar and "Fleetwood Mac it", spawning a 45-minute jam session as well as the demo of "It Ain't Me", a simple acoustic guitar recording with Tamposi on vocals.

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