"Birthday" is a song by American recording artist Selena Gomez for her solo debut album Stars Dance (2013).
The song was written and produced by Mike Del Rio, with additional writing by Crista Russo and Jacob Kasher Hindlin.
Matt Beckley provided additional vocal production for the song.
Musically, "Birthday" combines deep electronic dance beats and police sirens with elements of trap music.
The song's instrumentation is created by blending purring, synthesized bass, snappy beats, hand-claps, "oxygen-sucking" sub-bass, and trap snares with sexual moans and elements of hip hop music.