Knock Knock (Monica song)

"Knock Knock" is a song by American R&B recording artist Monica. It was written and produced by rappers Missy Elliott and Kanye West for her fourth studio album After the Storm (2003). Commissioned following the delay and subsequent reconstruction of Monica's third album All Eyez on Me (2002), the song is built around excerpts of the composition "It's a Terrible Thing to Waste Your Love" (1976) by American vocal group The Masqueraders. Due to the sample, Lee Hatim is also credited as a songwriter. The protagonist of "Knock Knock" warns a cheating boyfriend not to come calling.

J Records released "Knock Knock" alongside fellow Elliott production "Get It Off" as one of two singles that followed leading single "So Gone" during the third quarter of 2003. The song was lauded by critics, who praised its streetwise production and Monica's rap part on the track. A moderate success at the charts, it peaked at number 75 on the US Billboard Hot 100 and number 24 on the Hot R&B/Hip-Hop Songs chart. Its accompanying music video, directed by Chris Robinson, was filmed as a two-part story with "So Gone".