"Mr.Mr." is a Korean song recorded by South Korean girl group Girls' Generation for their fourth Korean titular extended play (2014). The song was released on February 25, 2014, as a single from the EP. The song was composed by American production team The Underdogs, who had previously worked with Western artists including Britney Spears, Beyoncé, and Justin Timberlake. A music video for the song was initially planned to be released on February 19 but was postponed to February 28 due to the accidental deletion of some of the original files.

"Mr.Mr." was described as an electropop and pop-R&B song that incorporates a hip hop beat and EDM-influenced buildups. The song received generally positive reviews from music critics, who praised its musical styles, which were deemed a departure from the group's signature bubblegum pop sound. The single ranked number 18 on Billboard magazine's list of 20 Best K-pop Songs of 2014 and was included on Time's list of 25 Best Songs of 2014 (So Far) in June 2014.

To promote the song and the EP, Girls' Generation appeared on several music programs including M Countdown, Music Bank, Show! Music Core, and Inkigayo around February and March 2014. The single was a commercial success in the group's native country South Korea, peaking atop the Gaon Digital Chart and selling over 900,000 digital units in 2014. It also charted at number three on the Korea K-Pop Hot 100 and number four on the Billboard World Digital Songs.

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