An architectural, urban planning and engineering firm, founded in Chicago by Louis Skidmore and Nathaniel Owings. In 1939, they were joined by engineer John Merrill. The firm's notable current work includes the new headquarters for The Walt Disney Company, Moynihan Train Hall and the expanded Penn Station complex, SOM has also designed some of the world's tallest buildings: John Hancock Center (1969, second tallest in the world when built), Willis Tower (1973, tallest in the world for over twenty years), One World Trade Center (2014, currently the seventh tallest in the world), and Burj Khalifa (2010, currently the world's tallest building).