President Barack Obama has nominated Janet Yellen, a renowned economist who serves as vice chairwoman of the Federal Reserve, to lead the central bank. "She doesn't have a crystal ball, but what she does have is a keen understanding about how markets and the economy work, not just in tech but the real world," Obama said. "She calls it like she sees it." Yellen's nomination has been warmly received. Christine Lagarde, managing director of the International Monetary Fund, says Yellen is an "excellent choice."