"Unfaithful" is a song by Barbadian recording artist Rihanna from her second studio album A Girl like Me (2006). Written by American singer and songwriter Ne-Yo in collaboration with its producers, Mikkel S. Eriksen and Tor Erik Hermansen, the song was released as the second single from the album on June 20, 2006 by Def Jam Recordings. "Unfaithful" is a pop ballad that contains prominent R&B characteristics, and was inspired by the works of American rock band Evanescence. Originally titled "Murderer", the song is about a woman who regrets cheating on her partner.
"Unfaithful" garnered a mixed response from critics; many praised its powerful balladry, but some criticized the lyrics. The song reached the top ten on the singles charts in 19 countries, including the UK Singles Chart, on which it became Rihanna's third top ten single. "Unfaithful" peaked at number six on the US Billboard Hot 100 chart and at number one on the US Hot Dance Club Songs chart. It was certified platinum by the Recording Industry Association of America (RIAA), denoting shipments of over one million copies.
The song's accompanying music video was directed by Anthony Mandler, and premiered in May 2006 on MTV. It features Rihanna in a love triangle in which she struggles to choose between her husband and her romantic interest, and regrets cheating on the former. Since its release, "Unfaithful" has become a staple of Rihanna's live performances. In 2006, she performed it on award ceremonies such as the MOBO Awards and the World Music Awards. The song was on the set list of her three major tours, Good Girl Gone Bad (2007–09), Last Girl on Earth (2010–11) and the Loud Tour (2011).