When in was constructed in 1974 it was the tallest building in the world, eclipsing New York's twin-towered World Trade Center by 25 meter. The observation deck, known as the sky-deck, is Chicago's most popular attraction, offering a view of the entire city. The sky-deck's attraction is a glass balcony which extends 4.3 feet, from where you can take a look straight down and see Wacker Drive and the Chicago river.

The name was changed from Sears to Willis as the Sears, Roebuck and Co. department stores moved from the building and London-based insurance broker Willis Group Holdings, Ltd. moved in. Even so, it is still referred to as the Sears Tower and there even is an online petition for keeping this name.