"Hello" is a song by British singer Adele. It was released on 23 October 2015 by XL Recordings as the lead single from her third studio album, 25 (2015). Adele co-wrote the song with her producer, Greg Kurstin. "Hello" is a piano ballad with soul influences, and lyrics that discuss themes of nostalgia and regret. Upon release, the song was well received by music critics, who compared it favourably to Adele's previous work and praised the song's lyrics and Adele's vocals.

"Hello" attained international commercial success reaching number one in almost every country it charted in, including the United Kingdom, where it became her second UK number-one single, following "Someone like You", and has the largest opening week sales in three years. In the United States, "Hello" debuted atop the Billboard Hot 100, becoming Adele's fourth number-one on the chart and breaking several records, including becoming the first song to sell over a million digital copies in a week. By the end of 2015, it had sold 12.3 million units globally and was the year's 7th best-selling single.

The accompanying music video was directed by Xavier Dolan and co-stars Adele and Tristan Wilds. The music video for the song broke the Vevo Record by achieving over 27.7 million views within a 24-hour span, held previously by Taylor Swift's "Bad Blood" which accumulated 20.1 million views in that timeframe. It also broke the record for shortest time to attain 100 million Vevo views, previously held by Miley Cyrus' "Wrecking Ball", as well as shortest time to reach 1 billion YouTube views (88 days). Adele promoted the song with a live performance on a BBC one-hour special, entitled Adele at the BBC.