British Airways (BA) is the flag carrier and the largest airline in the United Kingdom based on fleet size, or the second largest, behind easyJet, when measured by passengers carried. The airline is based in Waterside near its main hub at London Heathrow Airport. In January 2011 BA merged with Iberia, creating the International Airlines Group (IAG), a holding company registered in Madrid, Spain. IAG is the world's third-largest airline group in terms of annual revenue and the second-largest in Europe. It is listed on the London Stock Exchange and in the FTSE 100 Index.