"Mr. Taxi" is the first original Japanese song recorded by South Korean girl group Girls' Generation. It was released as a double A-side single with the Japanese version of "Run Devil Run" on April 27, 2011 as the third single from the group's eponymous debut Japanese album. Written by Allison Veltz, Paolo Prudencio, Chan Royce, and Scott Mann, and produced by STY, "Mr. Taxi" is an electropop and R&B song. A Korean version was later recorded and included on the group's reissue of their 2011 Korean album The Boys.

"Mr. Taxi" was a commercial success in Japan; it became the group's first single to sell 100,000 physical units in its first week of release. The single peaked at number two on the Oricon Singles Chart, number five on the RIAJ Digital Track Chart, and number one on the Japan Hot 100. It received certifications from the Recording Industry Association of Japan on four bases–physical sales (gold), digital sales (platinum), chaku-uta (double platinum), and full-length chaku-uta (double platinum). "Mr. Taxi" was also successful in Taiwan, on whose record chart it charted at number three. The Korean version peaked at number nine on the Gaon Digital Chart and sold over 1.5 million digital units in South Korea in 2011.

Proceeds of the single were announced to be donated to the Japanese Red Cross. The double A-side single contains a Japanese version of their 2010 Korean single "Run Devil Run" which was released as a digital single on January 25, 2011. "Mr. Taxi / Run Devil Run" was the first release by the group that contained an original Japanese song, as all previous releases by the group in Japan had been covers of their Korean songs, "Gee" and "Genie".

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