The Sears Tower is a skyscraper in Chicago, Illinois. It has been the tallest builing in the United States since 1973, surpassing the World Trade Center, which itself had surpassed the Empire State Building only a year earlier. Commissioned by Sears, Roebuck and Company, it was designed by chief architect Bruce Graham and structural engineer Fazlur Khan of Skidmore, Owings and Merrill.