Women start careers in business and other professions with the same level of intelligence, education, and commitment as men. Yet comparatively few reach the top echelons.

This gap matters not only because the familiar glass ceiling is unfair, but also because the world has an increasingly urgent need for more leaders. All men and women with the brains, the desire, and the perseverance to lead should be encouraged to fulfill their potential and leave their mark.

With all this in mind, the McKinsey Leadership Project—an initiative to help professional women at McKinsey and elsewhere—set out four years ago to learn what drives and sustains successful female leaders. We wanted to help younger women navigate the paths to leadership and, at the same time, to learn how organizations could get the best out of this talented group.

To that end, we have interviewed more than 85 women around the world (and a few good men) who are successful in diverse fields. Some lead 10,000 people or more, others 5 or even fewer. While the specifics of their lives vary, each one shares the goal of making a difference in the wider world. All were willing to discuss their personal experiences and...