Formerly Sears Tower
The Willis Tower, built as and still commonly referred to as Sears Tower, is a 108-story, 1,451-foot skyscraper in Chicago, Illinois. At completion in 1973, it surpassed the World Trade Center towers in New York City to become the tallest building in the world, a title held for nearly 25 years. As of December 2013, the Willis Tower is the second-tallest building in the United States and the twelfth tallest building in the world. More than one million people visit its observation deck each year, making it one of Chicago's most popular tourist destinations. The structure was renamed in 2009 by the Willis Group as part of its lease on a portion of the tower's space.