Title: Chairman, NBC Universal Cable Entertainment Group
Last year's rank: 33
Hammer received a hefty promotion in February. She now oversees 11 entertainment cable networks, including Bravo and USA, and two TV production studios. Revenue: about $5.5 billion. CEO Steve Burke often praises Hammer's Midas touch.
The Most Powerful Women in Business list is compiled by FORTUNE editors, who consider four criteria: the size and importance of the woman's business in the global economy, the health and direction of the business, the arc of the woman's career (resume and runway ahead), and social and cultural influence.