International Consolidated Airlines Group, also known as IAG, is an Anglo-Spanish airline holding company with its registered office in Madrid, Spain and its operational headquarters in London, UK. It was formed in January 2011 after a merger agreement between British Airways and Iberia, the flag carrier airlines of the United Kingdom and Spain respectively. British Airways and Iberia ceased to be independent companies and became totally owned subsidiaries of IAG, which was the sixth-largest airline company in the world in 2017.