"21 Questions" is a song performed by rapper 50 Cent. Nate Dogg, who gives additional vocals, is featured, but not credited, on the chorus and outro. The song was written by 50 Cent, K. Risto, J. Cameron, and V. Cameron for 50 Cent's commercial debut album Get Rich or Die Tryin'(2003). Released in 2003 as the album's second single, it became his second number one song in the United States after "In Da Club". It reached number six in the UK Singles Chart while "In Da Club" was at #23, giving him the rare feat of having two singles in the Top 30 at the same time. The track was produced by Dirty Swift and Bruce Waynne of Midi Mafia and samples elements from Barry White's "It's Only Love Doing Its Thing". R&B singer Lil' Mo created the answer-back remix titled "21 Answers". Her version received decent airplay, and was often merged together with 50 Cent's version for club play. While the title of the song is "21 Questions," 50 Cent actually asks 22 questions in the duration of the song.

When producer Dr. Dre worked with 50 Cent on his debut album, he stated that he did not want the song on the album. According to 50 Cent, "Dre was, like, 'How you goin' to be gangsta this and that and then put this sappy love song on?'" 50 Cent responded saying, "I'm two people. I've always had to be two people since I was a kid, to get by. To me that's not diversity, it's necessity."

The music video was directed by Damon Johnson, Dr. Dre and Phillip Atwell in March 2003. It depicts 50 Cent arrested and confined to prison, where he tries to keep in touch with his girlfriend, played by Meagan Good. In prison, he is constantly harangued by rival inmate, Tyson Beckford. The video ends with an alternate version of the beginning, showing 50 Cent and his girlfriend watching from their home as the police arrest Beckford instead of 50 Cent. The video has cameo appearances by G-Unit and Nate Dogg, who sings the chorus and the outro. The video concept can also be originated from Nate Dogg's "Never Leave Me Alone".

On April 15, 2003, the video debuted on MTV's Total Request Liveat number six, reached number one two days later, and stayed on the chart for fifty days. It also reached number two on the MuchMusicvideo charts.

A remix was released which featured American R&B singer Monica.