The ten tunes of U2's debut, Boy, are sturdily constructed and melodic. But by far the most arresting thing about the band is its sound. 

 The band as a whole suffers from sophomore slump on October. Bono seems particularly at a loss, making an impressive noise but precious little sense. 

 The EP Under a Blood Red Sky offers a glimpse of how U2's early sound translated in concert. 

 War is U2's first great record. Not only is the writing more tightly focused, but the band leaps nimbly between the personal and the political without a single misstep. 

 Producers Brian Eno and Daniel Lanois give The Unforgettable Fire a rich, atmospheric aura. The instrumental sound is blurred, giving the band a warmer, more intimate sound. This album also signals the start of Bono's obsession with America.  

 The intensely personal Joshua Tree album doesn't entirely avoid the political, but such concerns seem secondary to the quest for love and identity. Vivid as the album’s wordplay may be, it’s still the music that carries these songs. 

 At this point, the next logical move for U2 would have been a live album, but the bloated semi-live soundtrack album Rattle and Hum isn't quite what fans expected. 

 Thanks to the sound-shaping technology applied to the Edge's guitar and Larry Mullen's drums, the band's sound on Achtung Baby is more intricate and articulate than ever, affording the album broad stylistic range. 

 The quickly recorded Zooropa attempts to expand the band's new horizons even further, but gets mired in a quicksand of unwise groove and texture experiments–the result is an album with overlong, mostly unmemorable songs. 

 Pop puts more emphasis on the songwriting; the best song is the one that sounds the most like classic, pre-Achtung U2: the sweeping "Staring At the Sun." 

 If you happen to have been stuck in a soundproof chamber for the last few decades, U2's first two greatest-hits albums may prove useful in getting up to speed. The 1980-1990 collection spits (unforgettable) fire from start to finish. 

 After spending the Nineties dabbling in postmodernism, electronica and orange goggles, U2 transformed back to a world-beating pop band on All That You Can't Leave Behind, an album that oozed arena-scale romance. 

 If you happen to have been stuck in a soundproof chamber for the last few decades, U2's first two greatest-hits albums may prove useful in getting up to speed. 

 That was also the thrust of the enormous publicity push that accompanied the release of How to Dismantle an Atomic Bomb (which included a U2-themed iPod and The Complete U2, a 446-track digital "box set." 

 U218 Singles is a jumble of radio staples and two blah new tracks, one of which is a cover of the Skids' "The Saints Are Coming" recorded with Green Day. 

 U2 reunited with the Eno/Lanois team for most of No Line on the Horizon. Much of the album is relatively straightforward, but the songwriting was experimental and process-driven, integrating Moroccan music.