For as long as they’ve been making music, U2 have been afraid of being boring. That might sound like an odd thing to say of a band whose most recent album is a nearly three-hour, 40-track compilation of acoustic covers of their own back catalog, but the impulse to stun, bewilder, and confound has been an animating motivation since their formation in Dublin in the mid-1970s. It’s what excited the thunderous political ardor of War in 1983; what inspired their shift toward expressive watercolor grandeur on The Unforgettable Fire; what drove them to “go away and dream it all up again” after the landmark success of The Joshua Tree caused drummer Larry Mullen Jr., to worry that the band was “turning into the world’s most expensive jukebox.” Fear of being boring might be U2’s defining feature. And it is the essence of Pop.

“I do think that we live right now at a time, the fag end of the 20th century, where there’s a lot of nostalgia, and the musical climate is like karaoke,” Bono muses, voice even and eyes searching, halfway through U2: A Year in Pop, a 45-minute prime-time special that aired on ABC in the spring of 1997. “People aren’t liking things because they are great. They’re liking them because they remind people of something that was great.”

It was a complaint that Bono sounded often around the release of Pop, U2’s ninth studio album and—depending on what kind of U2 fan you ask—either their most interesting, most challenging, or least successful. In the wake of U2’s surprising reinvention as one of the most consequential popular rock bands of the 1990s, Bono had become enthralled by the pursuit of a freshly contemporary sound, and he had been pursuing it everywhere: in hip-hop and disco, techno and R&B. “When we’re at my house,” he told a reporter at the time, “it’s Sonic Youth next to Chic, into Dr. Dre or Wu-Tang Clan, into ‘Surf’s Up’ by the Beach Boys. Now, that might be a fucked up evening for some people, but that’s the way I live.”

Practically the only thing he wasn’t interested in listening to anymore was rock—it had become too stagnant, too resistant to change. “Y’know, what is rock music now? What is it?” he asked rhetorically in Q magazine. “Because there was once a time when people hadn’t heard the sound of an electric guitar overloading through a little printed circuit going into an amp. When people heard Hendrix, that was fresh.” You wouldn’t find that pioneering spirit listening to R.E.M. or Oasis, Bono felt. You had to look further afield. As he told Time, “White-bread rock has, for me, lost its sense of adventure, and seems very tired in comparison to hip-hop.”

Pop was U2’s effort to rediscover that sense of adventure. A playful, eclectic, sometimes abrasive synthesis of the band’s traditional songwriting instincts and their wide array of contemporary influences, including trip-hop, rap, and breakbeat, the album was not so much a stylistic departure as an attempt to demonstrate the breadth of what U2’s style could encompass. “The basic premise was that they wanted to move on, that they couldn’t repeat themselves,” Flood, one of its producers, said of the album. “They wanted to bring in elements from the dance world and integrate them, not necessarily with the aim of turning it into a danceable album, but to synthesize a new sound.” That synthesis could be unpredictable, but that was the point. “Half the time I didn’t have a clue what was going on,” Howie B, another producer, has claimed. “As long as you were able to react to what was happening and were honest, it was really exciting.”

On the final pages of U2: At the End of the World, Bill Flanagan’s book about the making of Achtung Baby, Zooropa, and the ZooTV tour, the author finds the band back in the studio in London, experimenting with Brian Eno and very slowly easing into writing and recording after a much-needed year of break following a long stretch on the road. “They will not officially begin a new U2 album until the spring of 1995,” Flanagan writes, while hinting that the work may have already nonetheless begun. That was November of 1994. Pop, their next album, would not be released until March 1997. “We have trouble finishing things,” the Edge admitted shortly before Pop debuted, during a time of 14- to 16-hour workdays, all-night recording sessions, and constantly shifting deadlines.

During the four previous years, the band had been working on almost anything other than a studio album. Bono and the Edge had written a James Bond song for Tina Turner (“GoldenEye,” for the movie of the same name). Adam Clayton and Larry Mullen, Jr., not to be outdone, had composed a new version of the Mission: Impossible theme for Brian De Palma’s cinematic reboot of the 1960s TV series. The whole band had come together to record “Hold Me, Thrill Me, Kiss Me, Kill Me,” for the Batman Forever soundtrack, and they had reunited with Brian Eno to record Original Soundtracks I, a record of theme music “for imaginary films,” released under the name Passengers. The latter is some of the most dynamic and rewarding music U2 ever wrote. Of course, at least one bandmember all but disowned it. “There’s a thin line between making interesting music and being self-indulgent,” Mullen said in 1997. “We crossed that several times on Passengers.”

But even once U2 began work on a proper album, frustrations rose and delays quickly mounted. Expect Nothing But the Best, as the record was rumored to be titled, was originally scheduled to be completed in the summer of 1996, with its lead single dropping in September and the album itself following in October. Those dates passed unceremoniously, as the press reported later in October that “the band was going back into the studio for more work and that a pre-Christmas release was out of the question.” According to an industry insider, as quoted in The Guardian, the delay was the result of “the band’s fantastically indecisive nature,” which made the group “quite capable of sitting around for four days wondering about it all and then recording on the fifth day.” Eventually, the release date was pushed to March.

It wasn’t a case of writer’s block that was causing the delay—as was widely reported, the band had written as many as 38 new songs by as early as the start of autumn ’96. It was instead a matter of deciding what they wanted their new album to say. The band was not inclined to rush it. “Sometimes it takes a few months for a record to focus,” the Edge told a reporter as what was now being called Pop was about to wrap. “You’ve got a lot of nearly finished ideas that could go lots of different ways, and then suddenly you see how things interact.” Or, as Bono put it to the same reporter, “Options are the enemy.”

But while this decision-making process could be drawn out, the band was still open to spontaneous change, as when they agreed—at practically the last moment—to put “If You Wear That Velvet Dress,” the planned B-side to the lead single, “Discotheque,” onto the album proper, forcing them to essentially improvise a substitute in the studio just days before the single was supposed to go to press. The replacement B-side, the sultry, propulsive “Holy Joe,” actually sounds more like it belongs on Pop than the moody, understated “Velvet Dress,” but that too was part of Pop’s ethos. “Flood’s philosophy is that the most interesting records are the ones where each track sounds different from the next,” mastering engineer Howie Weinberg explained.

The unifying idea was embodied by the meta-commentary of the title: Pop was meant to be an ironic celebration of consumerist spectacle, as if the band were putting air quotes around their own superstardom and gently mocking their status as “still the biggest, baddest band in the world,” as Dennis Hopper described them in A Year in Pop. They tried to emphasize this dimension of the album by making it the focus of the record’s promotional campaign and accompanying tour: When they called a press conference in 1997 to announce the launch of PopMart, they held it at the K-Mart store in midtown Manhattan, as if making a joke of their own success and ambition. “By holding your news conference in this setting, you don’t mean to suggest that your music is flimsily constructed from cheap materials, is discountable, and ultimately disposable, do you?” a reporter asked at the event. “I agree with everything you say,” Bono replied. “Apart from ‘discountable.’” It was all part of Pop’s winking meta act.

Like virtually every U2 album, Pop is somewhat front-loaded. “Discothèque,” which Bono has described as a way of getting “people dizzy so we can take advantage of them for the rest of the album,” announces the arrival of a new, upbeat U2 with a sugar rush of frantic energy, carried along by Clayton’s snaking bassline and Mullen’s club-ready beat (itself embellished by Howie B and Flood’s drum machines and cowbell). Contemporary reviews tended to deride Bono’s lyrics as self-consciously trite, compared to the earnest exhortations of “Pride (In the Name of Love)” or “One,” but the song’s ironic refrain, a jocular declaration that “you just can’t get enough of that lovey-dovey stuff,” is sly and suggestive in a way that Bono’s writing rarely is. The silliness is superficial; the song is subtler, and smarter, than, say, the po-faced “Yahweh.”

It’s on “Mofo,” the third track, that Pop most overtly shows off its influences, kicking off with a tidal wave of rhythmic distortion that’s somewhere between Massive Attack and the Prodigy. During the earliest Pop sessions, Mullen was sidelined with a nagging back injury; Howie B took advantage of the opportunity to fill in by allowing his turntables to serve as the drummer, much to Bono’s delight. The wall-of-sound approach to percussion that was born from these experiments is most apparent on “Mofo,” though Mullen did eventually replace many of the original drum machine tracks with his own attempts to replicate them on the kit. The flourishes that survive on the album track give the song a freshness that’s exhilarating.

In the months before release, rampant fan and media speculation about Pop had painted a picture of the album as U2’s Homework or Endtroducing…—an impression that lead single “Discothèque,” with its club-adjacent gusto, had done little to dispel. As if to bring listeners back down to earth, Pop follows “Mofo,” its most energetic and experimental song, with its most staid and traditional, the almost old-fashioned “If God Will Send His Angels,” which slows the tempo, stifles the irony, and gets the Edge back on stadium-licks form. It’s not a bad song; it’s sort of a lesser “Who’s Gonna Ride Your Wild Horses,” and it was understandably pushed as a single toward the end of the album’s life cycle, when its sales were in a slump. But it sounds a little flat after the ruthless boundary-pushing that precedes it.

“We didn’t set out to make a club culture record,” Bono has said. “We were just inspired by a lot of the music being made by hip-hop and dance artists and we wanted to explore some of those elements. But we still wanted to make a U2 record, and I think people will recognize that as soon as they hear the rest of Pop.” What Bono is imagining as the moment of recognition, one has to assume, is the back-to-back of “If God…” and “Staring at the Sun,” the closest thing Pop has to a “classic” U2 song by sound and reputation. Bono has elsewhere said that he wanted to avoid sounding like Oasis on Pop, but that’s what “Staring at the Sun” is most immediately reminiscent of: a big, crowd-pleasing barnburner, screaming for a drunken singalong.

“Gone” and “Miami” were both staples of the expensive, overstuffed Popmart tour, and both are rife with modern-sounding production elements that testify to U2’s commitment to experimentation. But they also reveal the limitations of the band’s magpie approach to production, and, smack in the middle of an hour-long album, they can’t help but feel like a mid-record slump. “Miami,” in particular, feels like a creative dead-end that should have been left in the studio: From its shifty, shuffling beat to its disruptive blasts of distorted guitar, it’s one of the rare moments on Pop where the songwriting is subordinate to the conceptual gimmickry. Bono’s wailed rhyme of “Miami” with “my mami” doesn’t help matters.

Pop reaches its climax with “Please,” a fairly straightforward song that gets a lot of mileage out of Flood and Howie B’s muscular production. There isn’t a trace of the dance or electronic music that Bono was obsessing over on this imploring, emphatic ballad, “a plea for sanity in the middle of war,” as Rolling Stone described it, that found new life in the wake of 9/11, during the band’s Elevation tour. Mullen Jr. has said that “Please” was “a great song” that didn’t “feel like it was finished,” but if it feels transitional, that’s because it seems to hint at the direction in which the band would soon be heading. For “Please” fans, “The Hands That Built America,” “Electrical Storm,” and many other similarly lugubrious songs were on the way.

“Already, U2 have been talking about taking a hard left turn away from the electric sass of their recent records,” a profile of the band revealed shortly after the release of Pop, amid the PopMart tour, “into something more organic and influenced by traditional Irish music.” Contemporary reviews of Pop had been enthusiastic, bordering on effusive; sales were strong, especially at the start. But it didn’t take long for U2 to have second thoughts about all this odd experimentation. The re-release of the Joshua Tree-era B-side “The Sweetest Thing” in 1998, as well as the ecstatic reception of their greatest-hits record, no doubt confirmed their suspicion: enough adventure. It was time to go back to basics. It was time for All That You Can’t Leave Behind.

But while history swiftly recast Pop as a failure—a foolhardy lark by a band of overambitious entertainers who had lost their way—it looks now, more than a quarter of a century later, like Pop was also U2’s last real effort to be bold and adventurous. “We were absolutely adamant that we didn’t want to sound like U2,” the Edge told a reporter about the making of Pop. “We’re so much better if we don’t know what we’re doing, because if it’s too easy, then that’s what it sounds like—too easy.” In the years after Pop, U2 knew exactly what they were doing, from the soaring chords of “Beautiful Day” to the D.O.A. boogie of “Get on Your Boots.” Pop was hard. The rest sounds easy.

Additional research by Deirdre McCabe Nolan.