Invensys plc is a British engineering company, heaquartered in London, England. It was formed by the merger of Siebe plc and BTR plc in 1999. The company is multinational with operations in over 60 countries, employing over 35,000 employees. Invensys is quoted on the London Stock Exchange as part of the FTSE 250 Index. As of March 2005, its market capitalisation is approximately £1.1 billion.