U2 were in a really rough place when they recorded October, their second album. Bono lost a suitcase containing all of his lyrics (it was recovered just a few years ago) and he, the Edge and Larry Mullen, Jr. were deeply immersed in a Christian organization called the Shalom Fellowship that made them question their decision to be in a rock band. Spiritual matters are at the core of several songs on the record, though "Tomorrow" is about the death of Bono's mother.

The disc wasn't a big seller, though "Gloria" did get some radio and MTV play. They rarely do any of this material in concert, though "Scarlet" was played a bit on the 360 Tour.

Pop has been unfairly dismissed as a disappointing U2 album. Part of this is the band's own fault. They made it very clear they were forced the rush the completion of the thing to accommodate tour deadlines, and they've remixed many of the songs on later compilations. The material is rarely played in concert and members of the band (especially Larry Mullen, Jr.) have slagged it off over the years.

It's not their best album, but songs like "Please," "Gone" and "If You Wear That Velvet Dress" are pretty brilliant. The album starts with dance songs like "Discoteque" and "Do You Feel Loved," and slowly gets darker and darker until it ends with a funeral on "Wake Up Dead Man." The critics tore it apart and the PopMart tour struggled to fill stadiums in America. It seemed like the band was finally on a downward trajectory, but U2 always does their best work when their back is against a wall.

With a new millennium looming and a (relatively) failed album in the very recent past, U2 decided it was time to strip things down. The winning production duo of Brian Eno and Daniel Lanois were brought back into the fold and they all wrote a series of songs that didn't sound like a band trying to burn down their past.

Crucially, All That You Can't Leave Behind doesn't evoke a single previous era of U2. Instead, these are simpler pop songs infused with the Edge's signature ringing guitar sound. This was the era of 'N Sync and Eminem, but the moment that "Beautiful Day" hit, it became a huge radio smash. "Walk On" and "Elevation" also became very popular and, suddenly, U2 were once again the biggest band on the planet. Tickers for their arena tour disappeared the moment they went on sale and it seemed like they were going to become the one rock group to keep making relevant music decades into their career. 

U2 were feeling bold after the huge success of Achtung Baby, so during downtime from their groundbreaking Zoo TV tour, they headed back into the studio to push the experimentation even further on Zooropa. Originally intended to be a mere EP, they wrote so many great songs, they decided to release another album in the summer of 1993.

The debut single, "Numb," was weirder than anything on Achtung Baby. It's basically the Edge rapping in a monotone voice, and the video showed the guitarist facing the camera while U2 and various models rubbed stuff in his face and tied him up. The album didn't produce any enormous singles, but tracks like "Zooropa" and "Daddy's Gonna Pay for Your Crashed Car" have aged very well.

Even the members of U2 admit that Rattle and Hum isn't the world's greatest rock documentary. It began as a very small project and somewhere along the way, it became a big deal, leaving virtually no one happy in the process.

That's not to say the soundtrack is a disaster. "Desire," "All I Want Is You" and "Van Diemen's Land" are fantastic songs, and it also has stellar live recordings of "All Along the Watchtower" and "Bullet the Blue Sky." Still, nothing could top The Joshua Tree and the press was more than ready to write the "U2 in Decline" story. In the end, it was a great learning process and it inspired them to really push the boundaries with their next work.

U2 had been around for nearly four years when they began recording their debut album, Boy, with Steve Lillywhite, but they'd only just begun to write truly great songs. Drummer Larry Mullen, Jr. was only 19 at the time and the others weren't much older, but constant gigging around Ireland had turned them into a tight unit.

The album begins with the classic "I Will Follow" and the 10 songs that ensue are largely about the process of boys turning into men. The influence of groups like Television and Joy Division was apparent, but it was very clear that this was a group with a unique sound and critics latched onto them right away. 

Many U2 fans have come to love October, but the band knew it wasn't their best work and they were determined to rise to the next level with their third album. Putting aside the spiritual matters of October, they wrote a strong collection of songs centered around the horrific political troubles in Ireland.

The very title of War makes the point quite clear, though many of the tracks deal with the emotional aspects of conflict rather than the overt politics. "New Year's Day" became their first American hit, and "Sunday Bloody Sunday" showcased the band at their absolute best. Bono began waving a white flag during their concerts and climbing high into the rafters. The album was a huge hit on college radio and MTV began airing their videos. 

After three straight albums with Steve Lillywhite, U2 decided to go in a different direction with their fourth album, The Unforgettable Fire, by bringing in the unique duo of Brian Eno and Daniel Lanois. Bono was inspired to write songs about the bombing of Hiroshima when he saw an exhibit about the attack in Japan called "The Unforgettable Fire."

Around the same time, Rolling Stone writer Jim Henke gave Bono a book about Martin Luther King, Jr. called Let the Trumpet Sound. It inspired him to write "MLK" and "Pride (In the Name of Love.") The latter became an enormous hit single and brought the band into arenas and the cover of Rolling Stone for the first time. The decade wasn't even half over, but Rolling Stone labeled them "Our Choice Band of the 1980s." It was a lot to live up to, but they pulled it off.

After a string of hit singles, a spotlight-stealing set at Live Aid and a triumphant Amnesty International tour with the Police, Peter Gabriel and Lou Reed, U2 were suddenly one of the hottest bands on the planet. Some groups wilt under that pressure, but U2 were determined to write a series of songs that lived up to the hype.

With the help of producers Brian Eno and Daniel Lanois, they created The Joshua Tree, an album that took over the entire planet in 1987. "Where the Streets Have No Name" might be the single greatest stadium rock song ever recorded, while "With or Without You" is the best prom song of the decade. "Bullet the Blue Sky" is a brutal condemnation of Ronald Reagan's foreign policy in South America, while "The Mothers of the Disappeared" is a mournful ode to the young men tortured and killed during Augusto Pinochet's brutal reign in Chile. These are some serious topics, but they caught on in a huge way and U2 suddenly found themselves on the cover of Time magazine. 

The four members of U2 instinctively knew that the 1990s were going to be a very different musical decade than the 1980s. Mega-1980s groups like Dire Straits, INXS, Poison and Bon Jovi were happy to simply repeat past successes in the new decade, but U2 knew they had to completely reinvent themselves in order to survive in this new world. They headed over to Germany right as the Berlin Wall was coming down and holed up at Hansa Tonstudio, where David Bowie and Iggy Pop worked in the 1970s. The place was falling apart and tensions nearly caused the group to split, but everything turned around when they stumbled upon the melody for "One."

They went back to Dublin and crafted an album that was the opposite of everything they did in the 1980s. This was music you could almost dance to; drawing influence from German techno, Euro-disco and Krautock, Achtung Baby sounded like the music of the future. It shocked critics and fans, eventually selling million of copies and guaranteeing that the band had an extremely bright future.