1997–2002

After taking a break in 1996, Green Day began work on a new album in 1997. From the outset, both the band and Cavallo agreed that the album had to be different from its previous records. The result was Nimrod, an experimental deviation from the band's standard pop-punk brand of music. The new album was released in October 1997. It provided a variety of music, with everything from upbeat pop-punk, laid-back surf rock, and peppy, silly ska, to an acoustic ballad. Nimrod entered the charts at number 10, partly because of the popularity of the acoustic ballad Good Riddance (Time of Your Life). The success of Good Riddance (Time of Your Life) won the band an MTV Video Award for Best Alternative Video for the song's video, which depicted people undergoing major changes in their lives while Billie Joe Armstrong strummed his acoustic guitar. The other singles released from Nimrod were Nice Guys Finish Last, Hitchin' a Ride and Redundant.

In 2000, Green Day released Warning, a step further in the style that they had hinted at with Nimrod. Critics' reviews of the album were varied. All Music Guide gave it 4.5/5 saying Warning may not be an innovative record per se, but it's tremendously satisfying. Rolling Stone magazine was more critical, giving it 3/5, and saying Warning... invites the question: Who wants to listen to songs of faith, hope and social commentary from what used to be snot-core's biggest-selling band? Though it produced the hit Minority and a smaller hit with Warning, some observers were coming to the conclusion that the band was losing relevance, and a decline in popularity followed. While all of Green Day's past albums had reached a status of at least double platinum, Warning was only certified gold.

At the 2001 California Music Awards, Green Day won all eight awards that they were nominated for. They won the awards for Outstanding Album (Warning), Outstanding Punk Rock/Ska Album (Warning), Outstanding Group, Outstanding Male Vocalist, Outstanding Bassist, Outstanding Drummer, Outstanding Songwriter and Outstanding Artist.

The release of a Greatest Hits compilation, International Superhits!, and an assemblage of B-sides, Shenanigans, followed Warning. International Superhits and its companion collection of music videos, International Supervideos!, sold reasonably well, going platinum in the U.S. Shenanigans contained some of the band's b-sides, including Espionage which was featured in Austin Powers: The Spy Who Shagged Me and was nominated for a Grammy for Best Rock Instrumental Performance.

In the spring of 2002, Green Day co-headlined the Pop Disaster Tour with Blink-182. Despite the co-headlining title, Green Day would play each show before Blink-182, who at the time were experiencing more success. The tour was documented on the DVD Riding In Vans With Boys.