Skidmore, Owings &amp; Merrill

Skidmore, Owings &amp; Merrill LLP (SOM) is an American architectural, urban planning, and engineering firm. It was formed in Chicago in 1936 by Louis Skidmore and Nathaniel Owings; in 1939 they were joined by John O. Merrill. 
The firm opened their first branch in New York City in 1937, and has since expanded offices in San Francisco, Los Angeles, Washington D.C., London, Hong Kong, Shanghai, Mumbai and Dubai.
SOM is one of the largest architectural companies in the world. They have designed several of the tallest buildings in the world, including the John Hancock Center (1969, second tallest in the world when built), Willis Tower (1973, tallest in the world for over twenty years), and Burj Khalifa (2010, currently the world's tallest building).