"We Belong Together" is a song recorded by Mariah Carey for her tenth studio album The Emancipation of Mimi(2005) and released as the album's second single in 2005. Written and produced by Carey, Jermaine Dupri, Manuel Seal, and Johntá Austin, the song was inspired by 1980s R&B and soul. Its arrangement is built on simple piano chords and an understated backbeat, and its lyrics chronicle a woman's desperation for her former lover to return after their separation. Billboard magazine named it the most popular song of the 2000's and most successful song by a female artist in Billboard history.

Following a career-decline between 2001 and 2005, Carey achieved major worldwide success with "We Belong Together" as the song topped the charts in Australia and the United States (for 14 non-consecutive weeks). In the U.S., the song also repeatedly broke many BDS Airplay records and was warmly received by critics. It won Carey a number of industry awards, including two Grammy Awards in 2006. Billboardmagazine listed "We Belong Together" ninth on The Billboard: All-Time Hot 100 Top Songs and the most successful song of the 2000s decade.

"We Belong Together" was not composed until late into the production of The Emancipation of Mimi. Following an unsuccessful career period between 2001 and 2003, Carey began production on the album in 2004. By November of that year she had considered the album complete, but some of what became its more popular tracks had yet to be written. L. A. Reid, the chairman of Island Def Jam Music Group, encouraged Carey to attempt additional studio sessions with producer Jermaine Dupri. "L.A. was like, 'You and Jermaine Dupri make magic together, why aren't you in the studio with him?'" she recalled. "'I said, 'I love Jermaine, is he free? I know he's doing a million things.' [...] But Jermaine said, 'Come on down.'"

Carey flew to Dupri's Atlanta studio and after two days, they composed two tracks for The Emancipation of Mimi("Shake It Off" and "Get Your Number") and she returned to New York City; however, at this point "We Belong Together" was still not written. Reid was impressed with the album's new material and decided that Carey should return to Atlanta to compose more tracks.

In another two-day studio stint Carey, Dupri, Seal and Austin produced the album's first single "It's like That" as well as "We Belong Together". The composers discussed the song's melody at length, and subsequently simplified the arrangement in order to accentuate Carey's vocals.

"We Belong Together" is a pop ballad that exhibits strong influences from hip hop and R&B. The song is propelled by a programmed Roland TR-808-styled kick and hi-hat, which is prominently utilized in hip hop music.

Carey adopts a reserved, rap-flavored singing style, which garnered approval from the critics who admonish her ornate, melismatic singing style. Reviewer Jennifer Vineyard comments that Carey's spare and understated singing approach gives the song more power, which would not have been achieved if Carey had belted. Besides hip hop, the song incorporates 1980s retro-soul music by "cleverly" referencing Bobby Womack's "If You Think You're Lonely Now" (1981) and The Deele's "Two Occasions" (1987, with Babyface). In the second verse of "We Belong Together," Carey sings: "Bobby Womack's on the radio/ Singing to me, 'If you think you're lonely now'." She then flips across a radio dial: "So I turn the dial, tryin’ to catch a break/ And then I hear Babyface/ 'I only think of you...'." Due to the inclusion of the lyrics from both songs, the songwriters were given co-writing credits on "We Belong Together."

"We Belong Together" comprises a very simple and understated musical arrangement: it is set in C major and is composed in 4/4 time. Similarly, within the song, Carey's vocal range spans from G ₃to A ₅. Carey's vocal range is demonstrated with a greater emphasis in the ending chorus, where the chorus is raised an octave higher, lying from G ₄to A ₅. As such, Carey ends with an anticipated coda, completing both the chorus and the entire song with a potent and unequivocal belted note of C ₅for approximately four semibreves. It follows the common verse-chorus form and is structured into three sections that portray the protagonist in a range of emotions; from doleful and resigned in the first section, to desperate and agitated in the second. In the last section the song climaxes with an octave raise, which not only emphasizes the protagonist's heightened desperation, but her determination to be with her lover.

Carey has often recorded remixes for some of her more popular songs, some of which have become more successful than their original counterparts. For "We Belong Together," she recorded the DJ Clue remix, which was produced by DJ Clue and features rappers Jadakiss and Styles P, and the Peter Rauhofer Reconstruction Mix/Atlantic Soul Vocal Mix. The remixes are fundamentally different from the album version and contain more distinct elements of hip hop music. The Atlantic Soul Vocal Mix, for example, features a synthetic bass line, a piano and guitar line, and distinctive hi-hats that produce a more up-tempo, hard-hitting beat.

Both remixes were offered as downloads in May 2005, and achieved success: the Atlantic Soul Mix reached number 1 on the U.S. Hot Dance Club Songs chart, while the DJ Clue version peaked at number 5 on the Hot Digital Songs chart.

The song's music video was directed by Brett Ratner and filmed in Los Angeles. It serves as the sequel to the video for "It's like That," the first single released from The Emancipation of Mimi. Beginning with the "It's like That" video, the protagonist is at her bachelorette party, where one of the guests reveals himself as a former lover (played by Wentworth Miller). The video for "We Belong Together" begins the following morning, when the protagonist remembers her former boyfriend, as she is preparing for her wedding. As she marches down the aisle, the protagonist debates whether she belongs with her former boyfriend or her fiance (played by Eric Roberts). Once she reaches the altar, she catches sight of her former lover who is watching the wedding from a distance. She runs from the ceremony and into his arms, shocking everyone at the wedding. The video is noted for the fact that Carey wore the same Vera Wang wedding dress that she wore at her wedding to Tommy Mottola in 1993.

The video reached number 1 on several video-chart countdowns, including BET's 106 & Park, MTV's TRL(where it retired after it remained on the countdown for fifty days), MuchMusic's Countdown, and VH1's Top 20 Video Countdown. VH1 named the song number 1 on its "Top 40 Videos Of 2005" in December of that year. By July 25, 2005 it was Launchcast's most-watched video of the year, with 7.5 million streamed performances. The video was nominated for "Best R&B Video" and "Best Female Video" at the 2005 MTV Video Music Awards.

"We Belong Together" became a "career re-defining" song for Mariah Carey at a point when many fans and critics had considered her career over.

Unlike most of Carey's more recent singles, "We Belong Together" received generally positive reviews from critics, most of whom hail the song as a "return to form," following reviews of Charmbracelet(2002) that suggested Carey had lost her signature vocal range and power. A review for Slant Magazine writes, "the...diva [keeps] cool with breathy, rapid-fire verses until the final full strong-voiced climax that... proves that 'The Voice' has indeed returned." They also said that "The song is as 'innovative' as Mariah has been in years" Other critics commended Carey on her novel singing style which, according to Kelefa Sanneh of New York Times, gives the song its propulsion. Similarly, Billboardmagazine and Johnny Loftus of Metrotimescharacterized the song as "perfect," "classy," and "sublime," while Pitchfork Media gave it four stars and a half.

Billboardlisted "We Belong Together" ninth on The Billboard Hot 100 All-Time Top Songs and second on Top Billboard Hot 100 R&B/Hip-Hop Songs. Blenderranked it fifteenth on its 100 Greatest Songs of 2005 list. Slant Magazine ranked it 2nd on their best songs of 2005 list. In Australia, the song finished 14th on ARIA Top 100 Singles of 2005 Chart.

Between 2001 and 2003, Carey's popularity had substantially declined and many had considered her career over. However, after being released to North American radio on March 26, 2005, "We Belong Together" became the biggest success of Carey's career and for her label. The song spent fourteen non-consecutive weeks at number 1 on both the U.S. Billboard Hot 100 — after making its debut at number 81 — and on the Hot R&B/Hip-Hop Songs chart. It had major cross-over success, becoming the first song to simultaneously occupy the number 1 position on nine Billboardcharts on the week ending August 6, 2005: the Hot 100, Billboard Hot 100 Airplay, Hot R&B/Hip-Hop Songs, Hot R&B/Hip-Hop Airplay, Pop 100 Airplay, Top 40 Mainstream, Rhythmic Airplay Chart, Hot Dance Club Songs, and the Hot Ringtones charts. One week earlier, it had become the first song to top eight charts concurrently. According to Mediabase and Nielsen BDS, "We Belong Together" broke several airplay records in the United States: it gathered both the largest one-day and one-week audience total in BDS history, reaching 32.8 million and 223 million impressions respectively. To date, "We Belong Together" has been listened to more than 8 billion times in the U.S alone. It was certified 2x Platinum by the RIAA. On Billboard Hot 100 Year-end Chart of 2005, the song was declared the number 1 song, a career first for Carey. It's also ended at 2 on Billboard's Hot R&B/Hip-Hop Songs Year-end chart of 2005. The song was also declared the most popular song of the 2000's by Billboard magazine.

"We Belong Together" achieved success in several major non-U.S. markets. It debuted at the top of the Australian chart, where it remained for two weeks. It reached a peak position of number 2 for three weeks in New Zealand. Promotion for the song was strongest in the UK, where it debuted at number 2 behind Tupac Shakur's "Ghetto Gospel", selling 39,436 copies, only missing the top spot by 392 physical and digital sales. Across Europe the song was a moderate success. It reached the top five in Spain, Ireland, Netherlands, Denmark and Switzerland, top ten in Norway, and top twenty in France, Belgium, Sweden, Italy and Germany. On the Australia's ARIA Top 100 singles end of the year chart of 2005, "We Belong Together" was ranked 17 and 10 on the Urban singles end of the year chart. It was certified 2x platinum in Australia by ARIA and platinum in New Zealand by RIANZ.

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