"Warning" is the sixth studio album by the American rock band Green Day, released on October 3, 2000, by Reprise Records. Building upon its predecessor Nimrod, it eschewed the band's trademark punk rock sound and incorporated acoustic elements and pop and folk styles. Lyrically, the album contains more optimistic and inspirational themes compared to the band's earlier releases. Warning was also Green Day's first album since Kerplunk that was not produced by Rob Cavallo, although he was credited as executive producer.
Despite mixed criticism towards the band's stylistic change, the album received mostly positive reviews from critics, who praised vocalist/guitarist Billie Joe Armstrong's songwriting. Although it peaked at number four on the US Billboard 200, Warning represented the lowest commercial slump in Green Day's career, being their first album since signing to a major label not to achieve multi-platinum status. However, the album being leaked onto Napster three weeks before its release may have contributed to its low sales. The album has nonetheless been certified gold by the Recording Industry Association of America and has sold over 1.2 million copies as of 2012, with worldwide sales of 3.5 million copies.
After taking a break from touring in promotion of Insomniac, Green Day recorded the more experimental Nimrod. This record featured a wider variety of genres and included the acoustic hit "Good Riddance (Time of Your Life)." Vocalist/guitarist Billie Joe Armstrong recalled feeling anxious about the song's release due to its vulnerability, which sparked a desire for the band to expand their songwriting.
The band embarked on the Nimrod promotional tour, primarily featuring intimate shows. By the end of the tour, the band's audience had evolved, and punk rock was no longer as popular in the mainstream due to the rise of nu metal acts. This led to a sense of being at a crossroads for the band.
For Warning, Green Day initially opted to work with a different producer, Scott Litt, but had disagreements over the album's musical direction. The band eventually brought back Cavallo, with the group handling most of the production duties. Armstrong listened to Bob Dylan's Bringing It All Back Home during the album's writing and recording, which influenced its musical experimentation and socially conscious lyrics.
The band began work on the album two years before entering the studio in April 2000. They met five days a week to write and rehearse, with a strong work ethic emphasized by drummer Tre Cool. The album aimed to have each song stand out, and the band focused on creating a thoughtful tracklist.
With Warning, the band experimented with more acoustic guitars and aimed for a more aggressive, percussive sound. The title track exemplifies this with layered vocals and a riff influenced by the Kinks. Other tracks incorporated various instrumentation, including "Misery," which features mariachi brass, and "Waiting," influenced by Petula Clark's "Downtown." The lyrics of the album are more positive and uplifting compared to earlier work, with a blend of sarcasm and a glimmer of hope.
Warning also contains explicitly political themes, such as in "Minority," inspired by Armstrong's concerns about the 2000 U.S. presidential election. Some publications noted the departure from the band's punk rock roots, while others still labeled the album as punk rock or pop-punk, along with other genres such as power pop, folk punk, pop rock, and alternative rock.
