"Say Something" is a song by American indie pop duo A Great Big World from their debut album, Is There Anybody Out There? (2013). Written by the duo members—Ian Axel and Chad King—alongside Mike Campbell, the song was originally recorded by Axel for his solo album This Is the New Year (2011). It was later released as a single by the duo on September 3, 2013, by Epic Records. Following its usage on American reality TV show So You Think You Can Dance, the track gained attention from singer Christina Aguilera, who wanted to collaborate with A Great Big World on the song. Quickly afterwards, a re-recorded version of "Say Something" with Aguilera was released on November 4, 2013.

"Say Something" is a slow-tempo indie pop piano ballad which talks about a breakup, where the lover is implored to make a statement that could potentially reverse plans, with the singers expressing humility, sadness and regret. In the single version with Aguilera, she plays a ghost of the lover to whom the song is addressed as she traces the steps of the lead vocal. The song was praised by music critics for its powerful lyrics, the emotional composition and Aguilera's vocal delivery. At the 57th Annual Grammy Awards, the song earned A Great Big World and Aguilera a Grammy Award for Best Pop Duo/Group Performance.

"Say Something" did not sell significantly well until the version with Aguilera was available. It debuted at number 16 on the Billboard Hot 100 chart after A Great Big World and Aguilera performed the song on The Voice. It eventually peaked at number four and has since sold over four million copies in the United States. It also topped the singles charts in Australia, Belgium, and Canada. A music video was released on November 19, 2013, featuring the trio singing as people "act out the heartbreaking lyrics." To further promote "Say Something", A Great Big World and Aguilera performed the track at the American Music Awards of 2013.

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