"Birthday" is a song by American recording artist Selena Gomez for her solo debut album Stars Dance (2013). It was written and produced by Mike Del Rio, with additional writing by Crista Russo and Jacob Kasher Hindlin. Matt Beckley also 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, handclaps, "oxygen-sucking" sub-bass, and trap snares with sexual moans and elements of hip hop music. Sparse drum beats and vocal chants are woven throughout the song's composition, which has been described by critics as an electropunk and club-ready, with trap and dubstep elements. The song was originally announced as a single, but was never officially released from the album.