GlaxoSmithKline plc (GSK) is a British multinational pharmaceutical company headquartered in Brentford, London. It was the world's sixth-largest pharmaceutical company in 2014, after Pfizer, Novartis, Sanofi, Hoffmann-La Roche and Merck. It was established in 2000 by a merger of Glaxo Wellcome (formed from Glaxo's 1995 acquisition of Burroughs Wellcome) and SmithKline Beecham (from the 1989 merger of the Beecham Group and the SmithKline Beckman Corporation).