[Bill Gates] wanted me to stay working at Microsoft, but I didn't think he could be CEO and we could have the family life that we both had growing up, which is what we envisioned. I knew I would go back to work at some point later to some profession. I just didn't know what.

In the developing world, it's about time that women are on the agenda. For instance, 80 percent of small-subsistence farmers in sub-Saharan Africa are women, and yet all the programs in the past were predominantly focused on men.

In the developing world, they don't have smartphones yet. They have the older plastic phones, but women are saving money on those, because they don't have access to banks. Having that access to digital money changes everything for her because she actually doesn't have to negotiate with her husband, which she will tell you is very hard in these circumstances, especially when the means are meager. She's expected to have money to pay for the kids' health or to help with the school fees.

All of a sudden people in the United States start to realize that vaccines make a difference. The controversy and the myth that's there, we're always trying to bust through that. So when I see a disease outbreak, I say to myself, "OK, that'll get people realizing how lucky we are to have vaccines."

Bill [Gates] and I believe philanthropy can only be effective if it starts things and proves whether they actually work or not. That's the place that governments often don't want to, or can't, work.

Philanthropy is not about the money. It's about using whatever resources you have at your fingertips and applying them to improving the world.

Women and girls face a whole host of issues. We start with health, so we work very deeply on maternal deaths, making sure that a mom doesn't die in childbirth, making sure that she has access, for instance, to AIDS medication.