"Iris" has contributed greatly to the band's success. Besides becoming one of the biggest alternative rock staples of the 1990s, "Iris" also remains one of the biggest crossover hits in the history of popular music, crossing over from modern rock radio to pop and adult contemporary radio, reaching number one on all of these formats and becoming the most played song of 1998 for all formats. The song reached number one in Australia, Canada and Italy, number three in the United Kingdom, number nine on the US BillboardHot 100, and has become one of Ireland's best-selling singles of all time. "Iris" is the Goo Goo Dolls' signature song, with critics describing it as an "ubiquitous" staple for the band's live sets.
"Iris" is a power ballad. In a 2013 interview with Songfacts, lead singer John Rzeznik explained how he wrote the song:
"I was thinking about the situation of the Nicolas Cage character in the movie. This guy is completely willing to give up his own immortality, just to be able to feel something very human. And I think, 'Wow! What an amazing thing it must be like to love someone so much that you give up everything to be with them.' That's a pretty heavy thought."
Upon its release, "Iris" became second of a string of hits from the film's soundtrack, City of Angels: Music from the Motion Picture. (The first was Alanis Morissette's "Uninvited" and the third was Sarah McLachlan's "Angel"). The song debuted at number 66 on the BillboardHot 100 Airplay chart on April 18, 1998, and eventually spent a record of 18 weeks at number one in Hot 100 Airplay. However it was not allowed to chart on the Billboard Hot 100 because no commercial single had been released. In December 1998, just after the song's airplay had peaked, the rules changed to allow airplay-only songs onto the chart. As a result, the song debuted and peaked at number nine and stayed on the chart for 14 weeks. On the Mainstream Rock Tracks chart, "Iris" peaked at number eight. The song was the band's 2nd number one hit on the Modern Rock Tracks chart, following their 1995 hit "Name." "Iris" stayed at number one for five weeks on the Alternative Songs chart and also hit number one on the Mainstream Top 40 chart for four weeks. The song spent a then-record 17 weeks at number one on the Billboard Adult Top 40 chart (beating No Doubt's 15-week run at number one with "Don't Speak" in 1996–97). The Goo Goo Dolls performed "Iris" on October 20, 2001 at Madison Square Garden as part of The Concert for New York City to raise money for victims of the September 11 attacks.
"Iris" was also a major international hit. It peaked at number five on the Irish Singles Chart and has since become the 19th biggest-selling single of all time in Ireland. The song initially peaked at number 50 in the United Kingdom in August 1998 before rising to number 25 the following year. On October 2, 2011, after performances by auditionees on The X Factor, the song re-entered the UK Singles Chart at number three. In May 2013, the song charted at number 12 after it was covered by Britain's Got Talent contestant Robbie Kennedy. Elsewhere, the song became a number-one hit in Italy (for four weeks), Australia (for five weeks) and Canada (for eight weeks), and it reached the top 10 in Flemish Belgium and the Netherlands.
Besides the song's success on the charts, "Iris" enjoyed critical acclaim. At the 41st Grammy Awards, "Iris" received nominations for "Record of the Year" and "Pop Performance by a Duo or Group." The song also garnered Johnny Rzeznik a "Song of the Year" nomination. The single was certified Platinum by the RIAA on August 18, 2008.
The song was ranked at number 39 on Rolling Stone's list of the 100 greatest pop songs.
In October 2012, "Iris" was ranked number one on Billboard's "Top 100 Pop Songs 1992–2012" chart, which ranked the top songs of the first 20 years of the Mainstream Top 40/Pop Songs chart. The list also featured the Goo Goo Dolls' hits "Slide", ranking at number nine, and "Name" at number 24. The Goo Goo Dolls are the only musicians to have three songs on the list, two breaking the top 10 and all three falling within the top 25. They are also the only musicians that have back to back singles (Iris, 1998 and Slide, 1999) featured on the list.