PepsiCo CEO Indra Nooyi retains her No. 2 rank, while DuPont chief Ellen Kullman rises to No. 3. Kullman displaces Hewlett-Packard chief Meg Whitman, who falls to No. 9.

At No. 4 is Marillyn Hewson, the CEO of Lockheed Martin , the world’s largest defense contractor.

Facebook COO Sheryl Sandberg (No. 5) and Yahoo CEO Marissa Mayer (whose turnaround effort has doubled the stock price and elevated her to No. 9) keep on climbing up the annual list, which Fortune launched in 1998.

So much for the notion that women aren’t gaining power in corporate America. Fifteen years ago, there were just two female CEOs of Fortune 500 companies. Today, there are 21. And in 1998, it took $1 billion or so to make Fortune‘s MPW rankings. A place on the 2013 list requires around $6 billion or more, depending on the health of the woman’s business. The highest-ranking newcomer: Lynn Good, CEO of the largest U.S. electric utility, Duke Energy , at No. 16.

Fortune ranks only women leaders in business, so Federal Reserve Chief nominee Janet Yellen would not make this list. Nor would a super-philanthropist such as Melinda Gates. Fortune‘s criteria for ranking include: the size and the importance of the woman’s business in the global economy, the health and direction of the business, the arc of the woman’s career, and social and cultural influence.

That latter factor boosted Sandberg this year. Her best-seller, Lean In, has sold more than one million copies since it was released last spring.

There’s never been anyone quite like Sandberg–billionaire best-selling author, world-famous feminist, and operating chief of one of the most important tech companies. This is why we put her on the cover of the 2013 Fortune MPW issue. If you want to understand Sandberg’s power and what she really does at Facebook, read my colleague Miguel Helft’s smart and insightful profile in the new issue. It’s the best MPW issue ever.