"Baby" is a song by Canadian recording artist Justin Bieber. It was released as the lead single from the latter half of Bieber's debut album, My World 2.0. The track was written by Bieber with Christopher "Tricky" Stewart and Terius "The-Dream" Nash, both of whom worked with Bieber on "One Time", and also by R&B singer Christina Milian and labelmate, rapper Ludacris.
It was available for digital download on January 18, 2010. The song received airplay directly after release, officially impacting mainstream and rhythmic radio on January 26, 2010. The song is uptempo R&B, blending together dance-pop and hip-hop elements, while using influences of doo-wop music.