Ne-Yo teams up with Kanye West to provide guest vocals on Keri Hilson's 2009 single "Knock You Down." The song is credited to Keri Hilson featuring Kanye West and Ne-Yo, making both artists prominent guest performers rather than background contributors.
The single was recorded for Hilson's debut album, In a Perfect World..., and was released in April 2009. Hilson sings the main sections, Kanye West delivers the opening rap and an interlude, and Ne-Yo performs the second verse and joins the closing vocal passages. The song combines R&B, hip-hop, and pop elements around the theme of love unexpectedly overwhelming someone.
Ne-Yo and Hilson already knew each other as professional songwriters, which helped make the collaboration natural. The track became Hilson's biggest solo hit, reaching No. 3 on the Billboard Hot 100 and No. 1 on the US Hot R&B/Hip-Hop Songs chart. The music video dramatizes a love triangle involving Hilson, West, and Ne-Yo, which can make the performers' roles easier to remember.