Forbes World's Most Powerful Women

Chancellor, Germany
German Chancellor Angela Merkel continues her reign as the most powerful woman on the planet for 10 years running. Why? She clinched a third four-year term of Europe's most vibrant economy in December 2014, making her the longest-serving elected EU head of state. She fought off a national recession during the global economic crisis with stimulus packages and government subsidies for companies that cut hours for workers, and she is in the thick of trying to help Greece revive its economy.

Chair, Federal Reserve, Washington, United States
Janet Yellen made history in 2014 when she became the first female head of the Federal Reserve. The Yale and Brown educated economist has barely had a moments rest since then: She took over shortly after the central bank began unwinding its recession era bond buying program and then deftly ushered markets through six cuts that brought monthly purchases to $0 from a peak of $85 billion. Now the Fed could loosen the economic reigns further by beginning to hike interest rates as soon as December 2015 -- a feat that was anticipated earlier in the year but hasn't attempted since 2004. With so much at stake a single word from Yellen can send asset prices swinging.

Managing director, International Monetary Fund
Christine Lagarde is entering the last year of her first term heading the International Monetary Fund, the organization which serves as economic advisor and backstop for 188 countries. When she took over in 2011 the world economy was still recovering from the financial crisis. Today Lagarde is projecting 3.5% annual global growth -- only a hint above last year's rate and down from 4% in 2011. Lagarde calls this the "new mediocre" and is vocal about her concern that slow growth has become the "new reality.

President, Brazil
Calls for President Dilma Rousseff's resignation were chanted through the streets of Brazil at the start of this year, just months into her second term. Rousseff, who ran on campaign promises to harness oil and boost the economy, is now battling a bribery scandal that involves the national oil company Petrobras. As Brazil's first female president, she was elected in 2010 and was on track to end poverty in the world's seventh-largest economy.

President, South Korea
Overseeing the world's 14th largest economy from the capital in Seoul, a mere 120 miles from her irascible and nuclear-tipped neighbor, Kim Jong-un, Park has the weight of the Sewol ferry tragedy and a massive bribery scandal on her shoulders. It's just over one year since the disaster killed more than 300 people and last month Park expressed "regret" over "prevalent, deep-rooted corruption" in the government.

Presidential candidate, United States
The presumptive Democratic front-runner in the 2016 presidential race started her campaign miles ahead of challengers. She faltered but has regained steam over time, putting up a strong front during an 11-hour marathon hearing before the House Select Committee on Benghazi. She is the first and only first lady to become a U.S. senator, not to mention presidential candidate. Her bestselling 2014 memoir, "Hard Choices," which chronicles her time as secretary of state, reportedly earned her a high-seven-figure advance.

CEO, IBM
More than three years have passed since Rometty took the helm at IBM and it's been anything but smooth sailing. With 11 consecutive quarters of revenue declines, IBM is sticking to its focus on boosting profit margins and cultivating growth. Under Rometty the technology giant has been shifting its portfolio of businesses. She has led spending programs for data-analysis software and skills, cloud computing and Watson artificial intelligence technology.

CEO, General Motors
Mary Barra survived a harrowing first year as the first woman ever to head a Big 8 automaker last year. She faced revelations about faulty ignition switches blamed for at least 74 deaths and 126 injuries, a 30-million car recall and pressure from investors to return more cash to shareholders. In October the 35-year GM veteran finally got to lay out her strategy for the future, which includes turning Cadillac into a global luxury brand, continuing to grow in China and becoming a technology leader.

Director-General, World Health Organization
Leader of the global health organization responsible for eradicating communicable diseases, including HIV/AIDS, tuberculosis, malaria, and other vaccine-preventable diseases, Chan is widely viewed as having fallen flat in her efforts to combat Ebola. Last year the outbreak in West Africa took the lives more than 10,000 people, while an estimated 26,000 cases were reported around the globe. After issuing a mea culpa for inadequate action, WHO is preparing advanced contingency and intervention plans for possible future epidemics of this magnitude.