Adele collaborated with various songwriters and producers, including Columbia Records co-president at the time Rick Rubin, Paul Epworth, Ryan Tedder, Jim Abbiss, and Dan Wilson.

A sleeper hit, it topped record charts in more than 30 countries and became the world's best-selling album of the year for both 2011 and 2012, helping to revitalise the lagging sales of the global music industry.

In addition, three of the five singles released in its promotion – "Rolling in the Deep", "Someone like You", and "Set Fire to the Rain" – became international number-one songs, while "Rumour Has It" charted in the top 20 in countries across Europe and North America.

[19] British producer Fraser T Smith recalled following a similar trajectory when he teamed up with Adele to compose the subsequent third single "Set Fire to the Rain" at his MyAudiotonic Studios in London.

Smith thought Adele's first attempt superior to subsequent takes and used the demo as the final production of the song, complete with live drum sounds and an elaborate strings section (arranged by British musician Rosie Danvers).

At the suggestion of Columbia Records group president Ashley Newton, she met with songwriter Greg Wells at his studio in Culver City, Los Angeles, where they co-wrote the gospel-tinged ballad "One and Only".

[23] The demos she had recorded with Epworth, Smith, and Tedder (including "Rolling in the Deep" and "Set Fire to the Rain") were subsequently rerecorded by Rubin when she met with him in his Shangri-La Studio in Malibu, California, in April 2010.

[12][17][24] Rubin, notorious for his unorthodox production style, pushed the singer beyond her comfort zone, and despite being drawn to his unconventional methods, Adele described working with the producer as daunting.

[24] Ultimately, she decided to scrap most of the work done in favour of the early takes she did with other producers, including Epworth and Tedder, in order for the music to reflect the raw emotion felt immediately after her break-up.

[26][34][35] Frequent smoke breaks with her tour bus driver,[23] a Nashville, Tennessee native, resulted in her introduction to bluegrass and rockabilly,[23] and the music of Garth Brooks,[23] Wanda Jackson, Alison Krauss,[26] Lady Antebellum, Dolly Parton, and Rascal Flatts.

[40] Jon Caramanica of The New York Times wrote that the album's music is a part of a recent British soul revival that "summoned styles dating back to Motown girl groups and Dusty Springfield".

[41] Ryan Reed of Paste calls Adele a "British alt-soul prodigy" and the album's music "the stuff of sensual modern pop-noir landscape, heavy on retro textures and relationship drama".

[11][43] Larry Flick of SiriusXM called 21 "a pop record with soul leanings", while The Washington Post's Allion Stewart commented on the album's eclectic nature: "Everything on [21] is precisely calibrated to transcend genres, to withstand trends ...

[45] The sequence of the tracks on the deeply autobiographical album correlates with the range of emotions Adele experienced after the break-up, progressing from themes of anger and bitterness to feelings of loneliness, heartbreak, and regret, and finally, acceptance.

[15][16] The revenge song "Rolling in the Deep," a "dark, bluesy, gospel, disco tune" in the singer's own words, was written as a "fuck you" to her ex-lover after his disparaging remarks that she was weak and that her life without him would be "boring and lonely and rubbish.

"[54] Jon Caramanica of The New York Times pointed out the song's "hollow counterpoint vocals" and slow, "daringly morbid" bridge that veers from the pounding rhythm before once again acceding to it.

"[42] The Rick Rubin-produced fourth track "Don't You Remember," co-written by Adele and Dan Wilson, marks a shift in the album's theme, from anger and defensiveness to reflection and heartbreak.

[60] Accentuated by ornate orchestral flourishes, swirling strings, crescendos,[37] and dramatic vocal effects towards its climactic end,[34] the song stands in stark contrast to the otherwise understated production of the album and, in reviews, was characterised by critics as a pop rock power ballad.

[34][61] "Take It All," the seventh track, written and recorded with Francis "Eg" White and Jim Abbiss before the breakdown of Adele's relationship, is a piano and vocal ballad that borrows heavily from pop, soul, and gospel.

[12][62][63] In his review of 21, Allmusic's Matt Collar called the song the album's centrepiece, "an instant classic" in the same vein as "And I Am Telling You I'm Not Going" and "All by Myself," a "cathartic moment for fans who identify with their idol's Pyrrhic lovelorn persona.

[70] Sean Fennessey of The Village Voice praised the singer's nuanced vocal performance in the song, which ascends "into a near-shrieked whisper" during parts of the chorus, after which she once again regains composure.

On 24 January 2011, during the week of the album's UK release, she performed an acoustic set of selected songs from 21 at London's Tabernacle music hall, which was screened live on her personal website.

[72] From September to October 2010, Adele embarked on a mini-promotional tour of the US, which included stops in New York and Minneapolis, as well as an exclusive appearance at the famous Club Largo in Los Angeles.

"[109] John Murphy of MusicOMH said that it shared the themes of "pain, sadness and anger" explored on Amy Winehouse's Back to Black (2006), while hailing 21 as "one of the great 'break-up' albums, and the first truly impressive record of 2011.

"[40] Sputnikmusic's Joseph Viney stated that 21 combined the "best bits of Aretha Franklin's old-school soul with Lauryn Hill's sass and sense of cynical modern femininity.

"[112] Ryan Reed of Paste regarded her voice as "a raspy, aged-beyond-its-years thing of full-blooded beauty",[42] while MSN Music's Tom Townshend declared her "the finest singer of [our] generation".

It also appealed to teens struggling with the first sting of heartbreak, hipsters who missed Amy Winehouse, traditionalists weary of synthesizers and vocal effects, and non-pop fans who simply found it refreshing to hear a singer belt out her blues with conviction.

[257][259] Ethan Smith of The Wall Street Journal found that Adele's "deliberately unflashy" nature, full figure, and "everywoman" appeal gave her a lucrative niche in the market,[36][260] while her tendency to emphasize "substance over style" made her the "Anti-Lady Gaga".

[260]With the release of 21, critics began to tout Adele as the new torchbearer for the British soul music that ascended to the American mainstream via Duffy, Joss Stone, Amy Winehouse and Lily Allen.

[266] In an article explaining Adele's record-breaking achievements and impact, The Recording Academy wrote that "Plenty of albums have tapped into emotional truths; few have endured like 21", and further commented that 21 "continues to resonate with audiences in 2021 as much as it did in 2011".