To mark the Gates Foundation’s 25th anniversary, I recently took a deeper dive into the progress we’ve made—and the challenges that remain—when it comes to saving children’s lives. One post looks back on how better data transformed our understanding of child mortality. The other looks ahead at innovations that could help millions more babies and mothers survive.

Immunizing children and supporting other health-related efforts—like fighting malaria, HIV, and tuberculosis—is the biggest focus of my philanthropy. I’m moved to act by the fact that roughly 5 million children under the age of 5 die every year, the vast majority of them in poor countries. Meanwhile, lifesaving tools like vaccines and medicines get developed for diseases that affect those who can pay, and not for ones that mostly affect people in poorer countries.

As a grandfather, I can’t imagine how awful it would be to lose a child, yet millions of families suffer that tragedy every year simply because of where they live. Fixing this disparity is the chief reason the Gates Foundation exists. I go to work each day thinking about how I can help close the gap.