It was certified platinum by the Recording Industry Association of America (RIAA), denoting shipments of over one million copies.

It features Rihanna in a love triangle in which she struggles to choose between her romantic interest and her lover, and regrets having cheated on the former.

After moving to the US, Rihanna signed a contract with Def Jam Recordings, and released her debut album Music of the Sun (2005).

"[3][4] Ne-Yo and Norwegian production duo Mikkel S. Eriksen and Tor Erik Hermansen collectively known as Stargate wrote "Unfaithful", which Rihanna explained was "new ground for [her]" because it was a ballad.

[7] Seven digital remixes of "Unfaithful" were released on July 17, 2006, via iTunes in several countries including France, Germany, Italy, Spain and the US.

[8] A CD single of the song, comprising its album and instrumental version, a Tony Moran's radio mix, and its music video, was released in the United Kingdom on July 25, 2006[9] and in August of that year in Germany and France.

[6][13][14] Originally, it was a dark and moody track inspired by the music of the American rock band Evanescence, with the working title of "Murderer".

[16] According to Brandee J. Tecson of MTV News, "Unfaithful" is a "bittersweet ballad" that shows a new side to Rihanna.

[12] Slant Magazine's Sal Cinquemani stated, "The melodramatic, string-laden ballad 'Unfaithful' is, if nothing else, an ambitious second single for an artist like Rihanna, and with lyrics like 'I don't want to be a murderer/Our love, his trust/I might as well take a gun and put it to his head,' it earns bonus points just for being so fucking weird".

[19] Steve Jones of USA Today wrote that while the other ballads on the album were not as strong, "'Unfaithful', in which [Rihanna] deals with the consequences of her own cheating heart, shows depth".

[20] Celia San Miguel from Vibe praised "Unfaithful", stating that it gives Rihanna a "new found charisma, solid vocal range and her ability to channel deep-rooted emotions with ease".

[22] A reviewer from Billboard magazine likened "Unfaithful" to Beyoncé's music and concluded that the song reveals Rihanna as a "young vocalist growing into her own".

[23] In an interview about Ne-Yo's work, Idolator's Maura called both "Unfaithful" and Beyoncé's "Irreplaceable" "ear-candy triumphs".

[24] Quentin B. Huff of PopMatters criticized the song's lyrics and described them as well-intentioned but "overboard with melodrama" and "devoid of remorse".

[30] The song was certified platinum by the Recording Industry Association of America (RIAA) on July 27, 2006, after more than one million downloads were shipped.

"Unfaithful" was certified gold by the International Federation of the Phonographic Industry (IFPI) – Switzerland for shipping over 15,000 paid downloads in the country.

She walks down the street and gets into a car with her lover, who is the note-writing diner from the restaurant and the man who plays the piano at the rehearsal.

[59] Rihanna opened the 2006 MOBO Awards on September 20, 2006 at the Royal Albert Hall in London with a performance of "Unfaithful".

[61] Her performance in Manchester was released in the UK through iTunes[62] and is featured on the Good Girl Gone Bad Live DVD.

[64] Her set list featured "Unfaithful" and other songs from her 2007 release Good Girl Gone Bad including "Don't Stop the Music", "Shut Up and Drive" and "Umbrella".

[64] Following the release of her fourth studio album, Rated R (2009), in the UK, Rihanna performed a Nokia promotional concert at the Brixton Academy in London.

[65] Rihanna performed "Unfaithful", and songs from her older releases, including "Disturbia", "Don't Stop the Music" and "Take a Bow", during this set.

[69] Rihanna performed the song on a levitating stage while wearing a long yellow dress and with a fan blowing her skirt up,[69] which Jon Bream of Minneapolis' Star Tribune said looked "like Celine Dion delivering 'My Heart Will Go On' on the deck of the Titanic".

[70] The Daily Record's Jules Boyle concluded that "tracks like 'Unfaithful' and 'Hate That I Love You' were suitably epic and backed with a full rock band.