More than three decades ago, each of us started a technology company based on a big idea—and each company found success based on a culture of innovation and accountability. In recent years, we've brought that same approach to our philanthropy and have joined forces on two major global projects: reducing tobacco use, which threatens to kill one billion people by the end of this century; and providing women with access to information and services they need to plan their families, leading to safer births and fewer maternal deaths.

Now,...