I've travelled extensively in the last 16 years - to slums in Bangladesh, to townships in South Africa, to all kinds of places in India, etc. When I would go and talk to villagers about something like vaccines, if I stayed long enough, the women would bring the conversation around and say: "What about this family planning tool? We can't keep having the number of children we're having."

Our economies are built on the backs of all this unpaid labor that women do.

We [with Bill Gates] started to make decisions about what we'd invest in. Then I actually started traveling for the foundation. I've probably been to India now eight times at least and Africa numerous times.

Even in our own agriculture strategy, if we got a great new drought-resistant seed and we managed to get it distributed in the system, we just assumed that it would reach female farmers. That's a false assumption, because women don't interact with agro-dealers. So if you don't develop specific programming to ensure that seed gets in a woman's hands, then the extra income [generated by higher-yielding crops] goes into her husband's hands.

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.

If you invest in a girl or a woman, you are investing in everybody else.

Men make different investments than women do. Women tend to invest more of their earnings than men do in their family's well-being - as much as 10 times more.