"XO" is a song by American singer Beyoncé from her fifth studio album, Beyoncé (2013). Columbia Records released the song as the lead contemporary hit radio single from the album in the US and Italy on December 16, 2013. Ryan Tedder co-wrote and co-produced "XO" with Terius "The-Dream" Nash and Beyoncé, with additional production handled by Chauncey "Hit-Boy" Hollis and HazeBanga Music. A pure midtempo pop love song, "XO" is complete with electronic musical instrumentation, synthesizers and drums. Musically, it was compared to Beyoncé's own song "Halo" and was noted for having several music hooks including its call and response chorus.

The usage of an audio sample from Space Shuttle Challenger disaster at the beginning of the song was criticized by the families of the lost crew, NASA, and some media. Beyoncé released a statement saying that the song was intended to help people who have lost loved people in their lives and that the sample was included as a tribute to the Challenger crew. "XO" managed to appear on many music charts across Europe and Oceania and it peaked at number 45 on the US Billboard Hot 100.

A music video for the song directed by Terry Richardson was filmed in Coney Island in late August 2013. It was made available on iTunes with the release of the album on December 13, 2013 and was released online three days later. Beyoncé performed the song during the last stops of the North American leg of The Mrs. Carter Show World Tour in December 2013 and later during the tour's second European leg in early 2014. To further promote "XO", she performed it at the 2014 BRIT Awards and later at the 2014 MTV Video Music Awards. Haim and John Mayer covered the song in 2014, with the latter releasing it as a single.

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