Written by Adele and the album's producer, Greg Kurstin, "Hello" is a piano ballad with soul influences (including guitar) and lyrics that discuss themes of nostalgia and regret.

[15] During the chorus, Adele is heard singing the lines over layers of backing vocals, piano and drums which were described by The Daily Telegraph as having "a very luscious wall of sound".

[10] Lyrically, the song focuses on themes of nostalgia and regret, and was seen as a follow-up to her single "Someone like You" appearing to reflect on a failed relationship.

The song's lyrics were also seen as being conversational, revolving around "all the relationships of her past", ranging from friends, family members and ex-partners.

[18] Josh Duboff of Vanity Fair wrote that "the Internet collectively lost their minds" after the broadcast of the trailer.

"[29] Writing for The Independent, Emily Jupp stated in her review of the song that it "might not be groundbreaking, but Adele's return with her familiar, smoky sound is very welcome".

She called it an "'if it ain't broke' ballad" and said: "Adele does what she does best, belting out emotional tales of love and loss much the same as with her last album, 21, but this time, with a little more self-forgiveness.

"[30] Greg Kot of the Chicago Tribune wrote: "Lyrics that work best when they zoom in on personal details match her combination of vocal power and restraint.

"[31] Neil McCormick from The Daily Telegraph called it "a beautiful song of loss and regret", adding that "it takes a grip on the kind of memory every listener holds somewhere in their heart and merges it with Adele's own drama.

[32] Several publications have commented on similarities in the theme of the song and accompanying video with that of "Hello" by American singer Lionel Richie.

Including streaming sales and excluding The X Factor and Pop Idol winners' singles, major charity campaign records and Christmas number ones, "Hello" was the second biggest selling number one of the 21st century in the UK, beaten only by Shaggy's "It Wasn't Me", which sold 345,000 copies in a week in February 2001.

[40] The song also debuted at number one in Belgium, Czech Republic, France, Germany, Greece, Hungary, Ireland, Israel, Italy, Lebanon, Luxembourg, The Netherlands, Norway, Portugal, Scotland, Slovakia, Spain and Switzerland.

[41] In Australia, "Hello" entered at the top of the ARIA Singles Chart on 31 October 2015, selling over 59,075 units, which earned the song a gold certification in its first week.

On the Radio Songs chart, "Hello" moved from 9 to 6, up by 46% to 106 million all-format audience impressions, thus becoming the top Airplay Gainer on the Hot 100.

By spending a tenth week at the top of the chart, it became Adele's longest-running number-one single and the longest-leading Hot 100 No.

[49] The single also benefitted from numerous Dance/EDM remixes as well,[50] thus resulting in "Hello" topping Billboard's Dance Club Songs and Dance/Mix Show Airplay charts.

[56] At the 2016 Billboard Music Awards, the singer was nominated for nine categories, winning five, including Top Selling Song for "Hello".

[60] Adele is the first artist in Grammys history to sweep the Big Three awards – Album, Record and Song of the Year – twice.

According to Dolan, Adele called him after an unspecified incident of police brutality in the United States, suggesting that a white male not be cast as her love interest in the video.

Dolan elaborated "She was just like, 'I'm concerned with the reality of the tensions between authorities and the black community, and I want to send a message out there.

[95] During the filming, both Adele and Wilds were asked to improvise and "tap into" their past relationships to convey the correct emotions.

[95] The sepia toned video shows Adele performing the song in a small house and outside in a wooded forest, intercut with scenes of her making a tearful phone call and flashbacks to a past relationship with Wilds' character.

Dolan replied to the remarks by saying: "It makes me uncomfortable filming iPhones because I feel like I'm shooting a commercial.

"[97] The music video for "Hello" broke the previous Vevo Record by achieving over 27.7 million views within its first 24 hours of release.

This record was previously held by the music video for Taylor Swift's "Bad Blood", which had amassed 20.1 million views in its first 24 hours.