For nine years, Forbes has ranked the 100 most powerful women in the world. These are the women who adhere to the traditional classifications of power (political and economic might) and those who have risen to the top of the social and cultural landscape. It is our annual snapshot of women who impact the world. This year the list features eight heads of state -- including our No. 1 on the list, German Chancellor Angela Merkel (pictured here), 25 CEOs who control $984 billion in revenues and 11 billionaires -- including the richest woman in Silicon Valley, Laurene Powell Jobs. We feature some dozen entrepreneurs and 10 celebrities who do more than look good: they’re philanthropic do-gooders and entrepreneurial go-getters. Here, a guide to Forbes Power Women 2012. The World’s Top 10 Most Powerful Women: Angela Merkel - Chancellor, Germany Age: 58 The world’s No. 1 Most Powerful Woman for the second year in a row, German Chancellor Angela Merkel is the "Iron Lady” of the Europe and the lead player in the eurozone economic drama that continues to threaten global markets. As Greece, Spain, Italy and Portugal have teetered on the edge of an economic brink, she has vowed to do everything in her power to preserve the 17-country EU. Hillary Clinton - Secretary of State, U.S. Age: 64 In keeping with her reputation as a no-nonsense diplomat, Hillary Clinton is spending her final months as Secretary of State far from the campaign trail. Much of that time has been on the go: this year alone she’s travelled to 42 countries. Dilma Rousseff - President, Brazil Age: 64 The president of the world’s sixth largest economy is ambitious at the mid-point of her first term, launching two aggressive programs meant to reverse the still-strong but shrinking national GDP. A June poll put Rousseff’s approval rating at 77%, and she is predicted to win a second four-year term in 2014. Melinda Gates - Co-chair, Bill & Melinda Gates Foundation, U.S. Age: 48 When you have your name on the top of the world’s wealthiest and most generous private foundation, challenging the Vatican to reverse its position against birth control makes news. This summer Melinda Gates, a practicing Catholic, vowed to dedicate her life-- an additional personal $560 million--to improving access to contraception to women in some of the world’s poorest countries. Jill Abramson - Executive Editor, The New York Times, U.S. Age: 58 In year one as the first woman at the top of the New York Times masthead, Jill Abramson has shuffled senior editorial staff and captained the 161-year-old publication through an ongoing digital transformation. Now behind a paywall, NYT.com has recruited nearly half a million paid subscribers and attracts 44 million unique visitors worldwide each month. Sonia Gandhi - President, Indian National Congress Party, India Age: 65 Sonia Gandhi, the longest serving chief in the Indian National Congress Party history, has had to defend herself and the party after a spate of key assembly elections this year, blaming the drubbing on weak candidates and state party organizations. Last year the 65-year old widow of Rajiv Gandhi, the one-time heir to the Nehru-Gandhi political dynasty, successfully underwent cancer surgery. Michelle Obama - First Lady, U.S. Age: 48 More popular than her husband in this important election year, Michelle Obama’s positive approval ratings register at 66% while POTUS’s term average has hovered just below 50%. The First Lady keeps a high profile with her mission to end childhood obesity, her commitment to military families and her stylish fashion picks. Christine Lagarde - Managing Director, International Monetary Fund, U.S. Age: 56 The first woman to run the IMF has spent much of her first year on the job battling the debt crisis in Europe. She’s been pushing for debt-sharing and an increase in rescue funds from the European Union but has faced resistance from fellow power woman Angela Merkel, Chancellor of Germany. Janet Napolitano - Secretary of Homeland Security, U.S. Age: 54 The first female head of the Department of Homeland Security, a position she took after serving as the first female governor of Arizona from 2003 to 2009, Janet Napolitano is at the helm of the third largest department in U.S. politics. Sheryl Sandberg - COO, Facebook, U.S. Age: 43 After four years as Facebook’s COO--and shepherded the company through its much anticipated and critiqued $100 billion IPO in May--Sandberg was named to the social network’s board of directors in June. She is Facebook’s first female board member and owns nearly $1 billion of unvested stock in the company. Forbes.com