Media interest in Mrs Obama has been huge - helping her onto the list
US First Lady Michelle Obama is among the newcomers in a list of the world's most powerful women.
Mrs Obama made her debut at number 40 on the list for Forbes Magazine, while German Chancellor Angela Merkel took the top spot for the fourth time.
Only four UK women made the Top 100 - down from five last year. They were led by Anglo American chief executive Cynthia Carroll, in fourth place.
Forbes ranks its list using a mix of media "reach" and financial impact.
Other women from the UK on the list included Pearson boss Dame Marjorie Scardino (19) and the Queen (42).
Meanwhile Burberry chief executive Angela Ahrendts (70) made a return to the list after two years of absence.
'Running the world'
"We look at hundreds of women who are at the top of their fields in business, politics, and non-profits, and set them against one another to see how they rank in terms of power," said Chana Schoenberger, co-editor of the list.
TOP 10 MOST POWERFUL WOMEN
1. Angela Merkel (German Chancellor)
2. Sheila Bair (Federal Deposit Insurance Corp, US)
3. Indra Nooyi(PepsiCo, US)
4. Cynthia Carroll (Anglo American, UK)
5. Ho Ching (Temasek, Singapore)
6. Irene Rosenfeld (Kraft Foods, US)
7. Ellen Kullman (DuPont, US)
8. Angela Braly (WellPoint, US)
9. Anne Lauvergeon (Areva, France)
10. Lynn Elsenhans (Sunoco, US)
"In our sixth year of this list, we're finding increasing numbers of women who are running the world."
In this year's list there are 27 heads of large companies, and 10 women with the title of chancellor, prime minister or president.
Forbes said Ms Merkel had topped the list "after leading Germany out of recession earlier than expected".
As well as Mrs Obama, Iceland's first female prime minister, Johanna Sigurdardottir, made her debut on the list - mainly due to her being charged with getting her country's banking system back on its feet after Iceland was forced to rescue its three main banks last year.
"It's a good year for women in power. The economic turmoil means that companies and countries are frequently looking for a change, so I think we'll see opportunities for women leaders," added Ms Schoenberger.
Other newcomers include Chanda Kochhar, chief executive of ICICI Bank (20) and the prime minister of Bangladesh, Hasina Wajed (78).