At Fortune’s Most Powerful Women Summit earlier this month, the lauded philanthropist and co-founder of the Bill and Melinda Gates Foundation spoke to a crowd of prominent female executives about the importance of investing in women and girls around the world. “It’s not enough to just talk about women and girls,” Gates said. “We have to be willing to stand up and say, ‘I’m willing to fund some of these things.'” In a follow-up interview with Fortune this week, Gates expanded on her talk at the Summit and explained why she is focusing her efforts on supporting women and girls around the country.

Edited excerpts:

What surprised you the most from the interviews during the Summit?

I was struck—and really impressed—by the fact that even though it was such a large scale event, it really felt like a series of candid conversations. It managed to be personal. There was a broad range of professional experiences and impressive backgrounds on that stage, but the speakers did more than just share tips and insights.

When was the moment that you realized helping women and girls was essential to global development?

When I first began focusing on family planning, it became clear that if you want to make life better for a community, you should start by investing in its women and girls. When I talk to women, a universal desire is to bring every good thing to our kids. Women tend to spend their resources on their families—prioritizing things like healthcare, nutritious food, education, and all the building blocks of a thriving society. The way I think about it is that when we invest in women, we invest in the people who invest in everyone else. So when we match their commitment with our own, great things are possible.

You said on stage that we are not helping women and girls enough around the world “at scale.” What did you mean by that?

What I meant is that we—as a global community—have learned a lot of different ways to help women in a lot of different places. Of course, the instinct now is to scale up these solutions and get them to absolutely everyone—but that’s not always a simple process. It’s important to recognize that gender roles vary across cultures, and women’s lives and circumstances are so different. So helping women and girls at scale means spreading proven interventions that work—like family planning tools and financial services—but it also means working with women and men to develop solutions based on their own unique needs and preferences.

In all your travels around the world, where have you been most encouraged by the development of programs for women and girls?

This is a hard question to answer—and that’s a good thing, because there’s so much great work being done, it’s hard to choose. It’s less about a specific a policy or program that the development community is creating, it’s more about what women are creating for themselves. I see this all the time when I visit women’s groups—meetings of ten or twenty women who are coming together to support and empower each other. These groups are a really big deal in developing countries, because often the women who join them live in male-dominated societies where they spend the majority of their days in male-dominated households. But women tell me that when they spend time together in these groups, they see that they have a lot more power over their lives and their futures than they ever imagined.

When I was in Tanzania earlier this year, I met with women who were pooling their money and giving each other loans to start little business ventures—like buying chickens to sell eggs at market. I was so struck by how much hope there was in the air. These women could see a better life for themselves and their families, and they could see their own actions helping create that. If we match these women’s commitment with ours, really incredible things are possible.

Why do you think it has been so long since new types of contraceptives have been developed and why is it particularly important for women in developing countries?

Even though our existing forms of contraception aren’t great, as far the market is concerned, they’re good enough. Oral contraceptives and IUDs work pretty well in countries like the U.S. and in most parts of Europe, where it isn’t a big deal for women to get a prescription refilled or get to a doctor to have a device implanted. So there isn’t much market incentive for companies to begin researching innovative new forms of contraception. But in developing countries, these existing forms don’t work as well, because needs are different.

Women in developing countries tell us they want longer lasting forms of contraception that could be self-administered—which makes sense because it’s often harder for women in places where there isn’t much healthcare infrastructure to get to a clinic. So one thing our foundation is doing is making the investments that will create that market demand and turn the world’s greatest scientific minds to meeting the needs of the world’s poorest women and girls.

You also said on stage that you don’t get a “do-over” with your kids. What are some things you do to ensure you get it right the first time around?

Bill and I are lucky in that we both had really good examples to look up to in our own parents. Both of us grew up in really loving, supportive households that put a lot of emphasis on giving back, and that’s something we’ve tried to replicate for our own family. But honestly, sometimes it’s just the simple stuff. My own mom made a point to have a glass of iced tea with me after school each day so we could talk about what was going on in my life—what I was struggling with and excited about. I’ve tried to provide that same kind of support to my own kids, which sometimes means sharing a snack after school and sometimes means things like going to soccer games. My oldest, Jenn, just started college, and I’m on the phone with her as much as she’ll let me.

Who are some of the role models that have helped you in the development of the foundation?

There are so many people who are instrumental in our foundation—from incredible staff to our partners on the ground who are helping us achieve maximum impact to the people who have helped and inspired us. To single out just a few of my role models, Bill Foege is an epidemiologist who is going to go down in history for his role in eradicating small pox. He’s a giant in the field of public health and proof that the global health community can and should rally to meet ambitious goals.

In addition to being a fellow graduate of Duke, Paul Farmer is a physician who’s bringing medical care and compassion to people in some of the world’s poorest places. Molly Melching has spent more than 40 years in Senegal improving lives for some of the country’s poorest people by working together with communities so that change is driven from the center out, not the top down. They’re all heroes to me.

And lastly, I have to mention Mother Teresa, for inspiring the world to focus on the poor. My own commitment to service and social justice is deeply grounded in Catholic teachings, and Mother Teresa is really the embodiment of those values.

What is your career advice for young women?

My advice is to trust your own voice and trust your own instincts. When I went to business school and started thinking about what kind of leader I wanted to be, I worried a lot about whether my management and leadership styles were close enough to what I saw others doing. But when, over time, I developed the confidence to stop trying to emulate others and to lead in a way that felt comfortable and true to me, it made all the difference. So trust yourself and trust your own voice. Women speaking up for themselves and for those around them is the strongest force we have to change the world.