There was a precedent. Damon and his pals George Clooney, Don Cheadle, and Brad Pitt had used the release of Ocean's Eleven to highlight the tragedy in Darfur. They formed Not On Our Watch, a nonprofit organization dedicated to ending mass atrocities in Darfur and elsewhere around the world. Clooney has said that if fans are crazy enough to follow him, well, then he will take them to Sudan. Damon also feels that celebrity brings with it an opportunity to do good. "You start to feel a level of responsibility to direct attention to things that actually matter more than to silly things like who you're dating." (For the record, he's been married for almost three years and has a ten-year-old stepdaughter, a two-year-old daughter, and a baby due this fall.)

Damon talks about Africa with a passion that comes from spending time there. Never once during our conversation does he plug or even talk about a movie project. The actor says that his trips have made the solutions real to him, brought them to life. In Tanzania, for instance, he visited a clinic and spoke with a 21-year-old mother with a baby in her arms. The child was slack-jawed, his head lolling back and forth. "I thought he was going to die right in front of me," Damon says. When he asked if there was something he could do, the child's doctor said the baby was going to be fine: He had already received life-saving anti-malarial medicine. Damon spoke with the mother, who lived on less than a dollar a day in a village that was a two-hour walk away from the clinic, and learned that her other child had died from malaria. "Then I realized that because of President Bush's malaria initiative, this baby had survived," says Damon, referring to Bush's 2005 pledge to increase malaria funding by $1.5 billion over five years. "American taxpayer money saved this baby's life."

Damon believes in the power of travel to transform people. He wishes that Americans were less insular, and quotes the fact that only 21 percent of Americans have passports. "I think many of our problems as a country would be solved if people had thick passports," he says. "There's just no substitute for actually going and seeing things."

Contrary to what you might expect from a celebrity, Damon comes across as a regular—albeit very thoughtful—guy, grappling with the values of our fame-obsessed culture and asking soul-searching questions about how to raise his children. We talk about kids, and he tells me that he wants his to see the world. He describes how Cheadle took his own daughters to Johannesburg's Soweto slum while he was filming Hotel Rwanda. "He didn't even have to say, 'This is why you're lucky.' He just let them take it in," Damon says. Being such a successful actor, he knows that his own children "will have incredible advantages that I can't even imagine and that I worry about sometimes." Seeing the world, he adds, "is the way they will remain grounded"