"Bellyache" is a song by American singer Billie Eilish from her debut EP, Don't Smile at Me (2017). The song was released as the EP's second single on February 24, 2017, through Darkroom and Interscope Records.
It was written by Eilish and Finneas O'Connell, with production being handled by the latter. A midtempo electropop, R&B, and alternative hip hop song, it has hip hop, deep house and Latin macabre influences. Lyrically, the song is written from the perspective of a psychopathic murderer. A remix by Marian Hill was released on May 5, 2017. The song received mainly positive reviews from music critics, several of whom praised the production and lyrics.
The song was accompanied by a music video, which was released on March 22, 2017. In it, Eilish is depicted in an all-yellow outfit as she throws dollar bills in the air and dances along the highway. Although "Bellyache" did not enter the US Billboard Hot 100, it peaked at number three on the US Bubbling Under Hot 100 chart for 32 non-consecutive weeks, making it one of the longest running songs to chart there without ever entering the Hot 100.
The song entered the top 100 of charts in Australia, Canada, Ireland, Portugal, and Scotland. It was certified multiple platinum in Australia, the United States, and Mexico by the Australian Recording Industry Association (ARIA), Recording Industry Association of America (RIAA), and Mexican Association of Producers of Phonograms and Videograms, A.C. (AMPROFON).
Eilish included the song on the setlists of her 2019 When We All Fall Asleep Tour and her 2020 Where Do We Go? World Tour.