Carrying nothing more than a few small bags and a single guitar, the four members of U2 stand calmly in the terminal of Charles de Gaulle airport in the image on the cover of their latest album, All That You Can't Leave Behind. It is a classy black-and-white spread that strips away the disco balls and splashy hijinks that marked their work in the late 1990s, and leaves exposed a pensive and insightful U2, in the middle of their ever-changing career-long journey.

For Bono, the lead singer for the multiple Grammy Award-winning and chart-topping rock band U2, life has always been an exploration. Down city streets, through seedy bars, in churches and on the concert stage, he has spent 41 years looking for answers. And after all that time, he may not have found exactly what he's looking for, but he is not anxious to rush the search. He is navigating the same fundamental questions that have consumed him since his youth--how does one remain a spiritual being in the modern world?

"He has a tremendous love for the world," says Bill Flanagan, a U2 biographer and a friend of Bono. "He always wants to go through one more door, go around one more corner."

His search for answers has led him through the extremes of both modern materialism and devout spirituality, which are deeply entangled in his life.

U2's last three tours have increasingly been multimedia spectacles that rate as some of the most expensive in rock concert history. For his part, Bono has undeniably lived the life of a rock star.

"He is someone who is always leading the 4 a.m. expedition to find the last open pub," Flanagan says. "He is the life of any party."

But there is a more spiritual side to Bono as well. A devout Catholic, he and his bandmates dabbled in evangelicalism during their youthful days in Dublin. At that time, they were torn between their increasingly demanding rock lifestyle and their spiritual devotion.

"The band almost broke up after their second album because they had a crisis over whether being in a rock band is a valid way to spend a life," Flanagan says.

The crisis was overcome, but Bono still refuses to allow himself to simply enjoy the hedonist luxuries of rock stardom.

"He has a genuine conscience and is dealing with issues, like if you only have one life to live, can you spend that life in show business?" Flanagan says.

Bono does not let show business monopolize his time. He has maintained an intense devotion to political causes--avidly supporting Amnesty International, meeting with then-President Bill Clinton, British Prime Minister Tony Blair and Pope John Paul II, and lobbying for Third World debt relief.

"He feels a moral responsibility to do what he can to help people, whether by using his money or his public platform or simply his access to people," Flanagan says.

With the band's newest album, All That You Can't Leave Behind, Bono seems more willing than ever to sing about the complicated nuances of maintaining faith and hope in a world filled with pain.

The feeling of war-torn optimism permeates the lyrics. Bono sings as someone who has seen what is worst in the world and still finds a sublime beauty behind the tears. Throughout the album, there is a recurring message that even in the darkest moments, one can find the strength to stand tall and find hope.

This message comes from a well-traveled man who has seen his home country of Ireland torn apart by perpetual warfare, has spent time in Ethiopia volunteering to aid starving children, and has recently lived through the suicide of his good friend, INXS singer Michael Hutchence. When Bono writes about the pain and suffering in the world, he is not a distant artist, speculating at what is out there. He has been in the trenches, and has seen the horror firsthand.