Some of the worst human tragedies happening in the world today go on because we don't really see them. We rarely make eye contact with people who are suffering, so we act sometimes as if the people don't exist."

The speaker is Bill Gates, the world's richest man. At a gathering in Seattle, he is talking not as the Microsoft chairman but as a partner in an intense personal mission. For Gates and his wife, Melinda, alleviating inequities in global health and domestic education has become a life's goal.

Having endowed their foundation with close to $29 billion, the Gateses are on track to become history's greatest philanthropists. But they do more than just shovel money out the door. Experts praise the couple for their astute vision and their ability to mobilize others: "Even with this gigantic endowment," says Susan Schwab, president and CEO of the University System of Maryland Foundation, "they know they can't solve these problems alone."

Their commitment came from different sources. For Melinda, it was a vacation to Zaire, where she was struck by meeting women in extreme poverty. For Bill, it was reading that millions of children die every year from preventable diseases. "Melinda and I had assumed that if there were vaccines and treatments that could save lives, governments would be doing everything they could to get them to . . . people," Bill said at the World Health Assembly in Geneva. "We couldn't escape the brutal conclusion that . . . some lives are seen as worth saving and others are not."

From shock came action. They focused on the simple message that one life is worth no more or less than another. Frances Hesselbein, chairman of the nonprofit Leader to Leader Institute, says: "Sometimes people give in a very detached way, but there is something about what they are doing . . . that is the opposite of that. It is very involved and personal."

Both Gateses read scientific books and travel extensively in developing countries. They share a sense of urgency. "We're not doing enough in developing countries to distribute the therapies and practices we know are effective in fighting diseases such as malaria, tuberculosis, and HIV," the couple told U.S. News .

So far, the Gateses have committed over $9 billion in grants, and the impact on global health has been enormous. "When you put high-octane fuel on a campfire," says Nils Daulaire, president and CEO of the Global Health Council, "you get a big blaze."

Resources. Of course, there was progress in global health before the Gateses came along. But often projects would be limited to a small region because of a lack of resources, says Christopher Elias, president of PATH, a group that designs and implements global health programs. "Now," he says, "there is a more serious discussion about doing things at scale."

A $100 million HIV/AIDS initiative in Botswana, funded by the foundation and Merck & Co., will bring prevention and treatment to all the citizens of the country, where 36 percent of the population is infected with the virus. Fewer people than expected are seeking treatment because of social stigma and problems in healthcare delivery. But lessons have been learned. "This project has helped to clarify that you need a whole systems approach," Bill Gates says. "Not just cheap drugs."