USG Corporation, also known as United States Gypsum Corporation, is an American company which manufactures construction materials, most notably drywall and joint compound. The company is the largest distributor of wallboard in the United States and the largest manufacturer of gypsum products in North America. It is also a major consumer of synthetic gypsum, a byproduct of flue-gas desulfurization. Its corporate offices are located at 550 West Adams Street in Chicago, Illinois., Together with other construction products, USG's most significant brands are:, In December 2013, Warren Buffett's Berkshire Hathaway became the largest shareholder in the company when it converted USG convertible notes it had acquired in 2008 to common stock., In June 2018, USG entered into an agreement to be purchased by the German building materials company, Knauf. The deal closed in April 2019.