"Knock You Down" is a song by American singer and songwriter Keri Hilson, recorded for her debut studio album In a Perfect World... (2009). The song features guest vocals from Ne-Yo and Kanye West. All three artists co-wrote the song with its producer Nate "Danja" Hills, as well as Kevin Cossom and Marcella Araica. The song was released first released to rhythmic and urban airplay in the United States as the album's fourth single in the US, and it would later serve as the third worldwide single.

The song is a contemporary R&B and hip hop song, which includes elements of pop music. The lyrics of the song pertain to how love "knocks you down." Part of the song refers to Michael Jackson; coincidentally it was released at the time surrounding the death of the singer. The song received generally mixed to positive reviews, with critics divided as to whether Ne-Yo and West overwhelmed Hilson's appearance. However, reviewers also complimented that the song was radio-friendly. It was nominated for multiple awards, including Best Rap/Sung Collaboration at the 52nd Grammy Awards.

"Knock You Down" peaked at number one in New Zealand, and was certified Platinum by the Recording Industry Association of New Zealand. It also reached the top ten in Canada, Ireland, the United Kingdom, and the United States. The song's music video was directed by Chris Robinson. It sees Hilson caught in a love triangle with her former partner West, and new-found love Ne-Yo. The video received positive reviews, which appreciated the given performances given by the artists. Hilson performed the song a number of times, including television appearances such as on The Rachael Ray Show. She also notably performed the song at the 2009 BET Awards, where she used the Jackson reference of the song to give a tribute performance to the late singer.

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