The Willis Tower, formerly known as the Sears Tower, is a 108-story, 1,450-foot (442.1 m) skyscraper in Chicago, Illinois. The tower has 108 stories, though the building's owners count the main roof as 109 and the mechanical penthouse roof as 110. When it finished costruction in 1973, it beat the World Trade Center in New York City to become the tallest building in the world. It was the tallest building in the world for twenty-five years until the Petronas Towers were built in Malaysia. It was also the tallest building in the Western Hemisphere for 41 years, until the new One World Trade Center beat it in 2013.
Willis Tower is seen as the best work of architect Fazlur Khan. As of 2021, it is the third-tallest building in the United States and the Western hemisphere. It is also the 23rd-tallest in the world. Each year, more than one million people visit its observation deck, the highest in the United States. It is one of Chicago's most popular tourist places. The tower was renamed in 2009 after the Willis Group bought the tower.
The building's largest office partner is United Airlines, which moved its corporate headquarters from 77 West Wacker Drive in 2012. Other major company offices in the tower include Schiff Hardin and Seyfarth Shaw. Morgan Stanley moved into the tower in 2019.
It was known as the Sears Tower until 2009, as it was the headquarters of retail company Sears from its opening in 1974. Many people from Chicago still call the tower by its original name.