How to be a Fortune Most Powerful Woman: Step 1

We constantly field queries from PR specialists, HR bosses, CEOs, and even wannabe Most Powerful Women, who ask: How does one make Fortune's annual MPWomen list? Throughout this week, I'll give you the lowdown about how we select women leaders for the list, now 10 years old. First of all, I should tell you that the Fortune MPWomen lists -- ranking 50 women in the U.S. and 50 women who work outside the U.S. -- includes executives in for-profit companies only. So Hillary Clinton and Melinda Gates aren't even in the contest.

This is the first criteria we consider in evaluating the women: the size and importance of her business in the global economy. Example: Indra Nooyi, the chairman and CEO of PepsiCo (PEP), is the current No. 1 on the Fortune list. PepsiCo's heft -- $39.5 billion in revenues and $5.7 billion in net income last year -- gives her the edge over Xerox (XRX) CEO Anne Mulcahy. Why doesn't Wellpoint (WLP) CEO Angela Braly, who oversees $61.1 billion in revenues, outrank Nooyi? Because PepsiCo bests Wellpoint in stock-market value. And profits too.

P.S. In 1998, when we launched the MPWomen list, we chose a virtually unknown executive named Carly Fiorina to be the No. 1. Then president of Lucent's largest division, Fiorina had also overseen the company's IPO -- at the time, the largest in corporate history. Those were the days when telecom was red hot. So was Fiorina, whom we ranked above Oprah Winfrey and Jill Barad, Mattel's (MAT) then-CEO.