"No One" is a song by American R&B and soul singer–songwriter Alicia Keys from her third studio album, As I Am(2007). Written and produced by Keys, Kerry Brothers, Jr., and George D. Harry, and released as the album's lead single in September 2007, this is overall Keys' biggest hit to date, having topped several singles charts, including the Hot 100 for five consecutive weeks and the Hot R&B/Hip-Hop Songs for ten consecutive weeks. "No One" was ranked at number forty-two on The BillboardHot 100 All-Time Top Songs and number fourteen on the Top BillboardHot 100 R&B/Hip-Hop Songs. It is her second solo number-one single in the United States after 2001's "Fallin'". In 2009 the song was named number six on the BillboardHot 100 Songs of the Decade.

The song won Best Female R&B Vocal Performance and Best R&B Song at the 2008 Grammy Awards on February 10, 2008. During the ceremony, Keys performed it in a duet with John Mayer. "No One" was also the most listened song on U.S. radio of 2008 with 3.08 billion listeners.

Keys told MTV News Canada that the song "is really talking about the way that in relationships, the way that so many things are around you all the time to try to distract you. And even though people may talk and say whatever they may want to say, but then no one can get in the way of this."

The song was first heard in August 2007 after Keys included a clip of the song in a newsletter on her official website and fan club. It was released officially on September 10, 2007, and its radio premiere was on Atlanta's WVEE on August 29.

Keys performed a medley of "No One" with George Michael's "Freedom! '90" at the 2007 MTV Video Music Awards on September 9. Remixes of the song featuring Lil' Kim, Damian Marley, Junior Reid, Beenie Man, Barbee, and Kanye West exist. The official remix has a different but similar beat from the original version and features rapper Cassidy, it was produced by Swizz Beatz.

It was ranked at number three on the recap of The 10 Best Songs of 2007 by Entertainment Weekly, while it was voted number twenty-three in The Village Voice 's 2007 Pazz & Jop critics' poll (tied with Modest Mouse's "Dashboard", R. Kelly's "I'm a Flirt" (Remix) featuring T.I. and T-Pain, and Avril Lavigne's "Girlfriend").

With only one full day of airplay, "No One" debuted at number sixty-five on the U.S. BillboardHot R&B/Hip-Hop Songs chart the week of September 8, 2007. Seven weeks later, it reached the top position for ten weeks—becoming Keys' fifth number-one single on the chart—before being knocked out by her own song "Like You'll Never See Me Again" the first charting week of 2008. The song initially debuted at number fifteen on the Bubbling Under Hot 100 Singles the week of September 15, 2007, and managed to jump to the Hot 100 at number seventy-one the following week without the benefit of download sales. The following week, it rose to number fifteen because of digital downloads, and reached the top spot the charting week of December 1, 2007, staying atop for five weeks, preventing Timbaland and OneRepublic's hit "Apologize" from reaching the summit. It is Keys' first solo single to reach number one on the Hot 100 since her debut single 2001's "Fallin'" and her third single, to date, to top the chart. The song's success marked Keys' return to the top twenty of the BillboardHot 100 in three years; her last appearance occurred with the number-twenty entry "Karma". Furthermore, "No One" went on to top eleven other charts: the Hot 100 Airplay (for fourteen weeks in a row, the longest run atop the chart since Mariah Carey's 2005 hit "We Belong Together" spent sixteen weeks at number one), the Hot R&B/Hip-Hop Airplay, the Hot Adult R&B Airplay, the Pop 100, the Pop 100 Airplay, the Top 40 Mainstream, the Rhythmic Top 40, the Hot Digital Songs, the Hot Digital Tracks, the Hot RingMasters, and the Hot Videoclip Tracks. The song was ranked number three on the Top Hot 100 Hits of 2008.

"No One" was a massive success in Europe, reaching number two on the composite European Hot 100 Singles as well as topping the singles chart in Switzerland and Hungary, while charting inside the top five in France, Germany, Italy, Portugal, the Netherlands, Belgium, Austria, Sweden, Slovakia, and Turkey, and the top ten in the United Kingdom (where the single became Keys' first solo top ten hit since "Fallin'", peaking at number six, and sold in excess of 200,000 copies), Ireland, Spain, Denmark, and Norway. "No One" has re-entered the UK Singles Chart twice since its official release, both times due television exposure (firstly after being performed by an auditionee on Britain's Got Talentand secondly after Keys herself performed it within a medley on The X Factor). In May 2009 it re-entered at number fifty-four and in December 2009 it re-entered at number fifty-one. In total "No One" has spent twenty-nine weeks inside the UK top one hundred singles, making it by far her longest-charting single in the UK. It also charted highly in Oceania, spending three consecutive weeks at number three in Australia and six non-consecutive weeks at number two in New Zealand.

In the week between October 22–25, "No One" gained 14.3% in radio airplay and audience impressions which marks the single at number one. As I Amwas also at number one that week.

The song's music video, directed by Justin Francis, premiered on BET on September 24, 2007; it debuted on 106 and Parkat number ten the following day, and has since peaked at number one. It premiered on Yahoo! Music on September 25 at number five and peaked at number one, and it premiered on Total Request Liveon October 4 and peaked at number one. It debuted on VH1's VSpot Top 20 Countdownat number three, peaking at number one. The video was ranked at number twenty-two on VH1's Top 40 Videos of 2007 and at number two on BET's "Notarized: Top 100 videos of 2007".

The video for "No One" consists of four settings: the first one shows Keys lying on a chair in an empty room; the second one is a musical instrument-decorated room in which Keys sings accompanied by a keyboard; in the third one Keys is initially alone, playing the piano on a rainy street, and she later finds herself surrounded with dozens of people; in the fourth and final one Keys is in a blue-lit nightclub. The video ends with a gear divided into four fractions, each one featuring a previously shown setting, and with Keys lying on the chair in the same room shown at the very beginning of the video.

As of October 2009, the official video alone has had over eighty-four million views on YouTube, and peaks at number five on the website's rank of all-time most viewed videos as well as number four on the rank of all-time most viewed videos in the music category.

"No One" was used in the theatrical trailer for the 2008 romantic comedy film 27 Dresses, as well as in the Ugly Bettyepisode "Burning Questions", originally aired on May 1, 2008. Felicia Barton sang the song in the top 36 night on the March 3 show of American Idol. Ten-year-old Natalie Okri performed the song on Britain's Got Talentin auditions 6 of the show, which aired on May 16, 2009, receiving rave reviews from the judges and a standing ovation from the audience. In the 2009 film Alvin and the Chipmunks: The Squeakquel, The Chipettes sing the song with Filipina singer Charice Pempengco. This version was released on the film's soundtrack on December 1, 2009.