BILL GATES $200 BILLION MOONSHOT

INSIDE THE BIGGEST BET ON HUMANITY A PHILANTHROPIST HAS EVER MADE

- GEOFF COLVIN

IN OCTOBER, the boy wonder of software for the masses will turn 70.

At an age when many retire, Bill Gates can say he has changed the lives of a large portion of people on earth in some way, either through the personal computing software and technology he pioneered during his storied career at Microsoft, or through the public health and education work of the Gates Foundation, which has delivered lifesaving vaccines, medical innovations, educational reforms, and policy-changing research to the global poor for a quarter-century.

But his biggest impact is yet to come. In May, Gates made an astounding announcement: He said he will give “virtually all my wealth”—about $100 billion—to the foundation. This is the largest philanthropic commitment in modern history, and it will double the speed of the work the foundation is doing to cure preventable diseases that affect the poor around the world. It comes, however, with a caveat: That work must be completed, and the foundation's $200 billion (including its current endowment and projected growth) must be spent, in the next 20 years. Then the Gates Foundation will shut its doors for good.

That's unheard-of for a foundation of such size. Those created by John D. Rockefeller and Andrew Carnegie, for example, are still operating more than 100 years later. The Gates Foundation, having disbursed just over $100 billion in its first 25 years, will spend about $10 billion a year in its final 20 years—sums exceeding the entire foreign aid budget of all but the richest nations.

In two exclusive interviews with