"1 Thing" is a song written by American R&B singer and songwriter Amerie and Rich Harrison for Amerie's second studio album, Touch (2005). The song is influenced by go-go rhythms and features a prominent sample of The Meters' 1970 funk recording of "Oh, Calcutta!", written by Stanley Walden. Its lyrics focus on an unidentified "thing" that fuels a romantic attraction.

The song was released as Touch's lead single in 2005, and is the only single from the soundtrack to the 2005 romantic comedy film Hitch. "1 Thing" received acclaim from critics, and peaked at number eight on the Billboard Hot 100 and number four in the United Kingdom, becoming Amerie's first top ten single and her biggest hit to date, also peaking at number one on the U.S. R&B singles chart. Its digital download and ringtone releases were each certified gold by the Recording Industry Association of America.

The song earned Amerie a Grammy Award nomination for Best Female R&B Vocal Performance at the 2006 Grammy Awards. A remix of "1 Thing" features rapper Eve. It was later named the twenty-second and twenty-fifth best song of the 2000s decade by Rolling Stone and Robert Christgau, respectively.

In 2004, when working on her second album, Amerie enlisted the services of producer Rich Harrison, who had helped produce and write her first album. In May 2004, Harrison heard "Oh, Calcutta!" for the first time and began working on the beat accompanying the ten-second back-and-forth breakdown between Meters drummer Ziggy Modeliste and guitarist Leo Nocentelli. Harrison said he loved the work of the Meters, especially Modeliste, commenting, "Ziggy, he's crazy." He processed the way the breakdown could be "flipped", added a bongo drum, a cowbell, and a ride cymbal, and sent it to Amerie. According to Harrison, they wrote and finished the song in two to three hours.

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