In their new book, Half the Sky: Turning Oppression into Opportunity for Women Worldwide (Knopf), husband-and-wife Pulitzer Prize winners Nicholas Kristof and Sheryl WuDunn argue that the key to economic progress in the world lies in unleashing women's potential. Their suggestions for how you can help:

Make girls smarter. Many pregnant women living in poverty don't get enough iodine, so their fetuses' brains do not develop properly. Their children routinely lose ten to 15 IQ points—particularly the girls, for reasons not fully understood. The solution: Iodize salt, at the cost of a couple of pennies per person per year. To contribute, go to Helen Keller International (HKI.org).

Support a woman's business. With a microloan of $50, a woman can start a business, producing income she can use to feed her children and send them to school. To make a loan, go to Mercy Corps (MercyCorps.org) or BRAC (BRACUSA.org), two groups helping women around the world.

Keep a girl in school. A girl who gets an education will have fewer children, earn more money, and be able to help her younger siblings. One excellent support program operates in Cambodia, where uneducated girls are at great risk of being trafficked into brothels. For $10 a month, you can keep a girl in school through American Assistance for Cambodia (CambodiaSchools.com), or for $13,000, you can build an entire school that will revolutionize life in a village forever.

See 8 more ways of looking at power, and meet the 20 women who made O's first-ever power list.