United Airlines is one of the largest airlines in the world today, serving six continents and having the highest number of flights of any airline on Transpacific and Transatlantic routes. Today, its fleet has grown to over 800 aircraft, and its order book is significant, with Boeing having most of the orders. Late last year, United took delivery of its first Airbus aircraft in over twenty years, adding the A321neo to its operations. As one of the founding members of the Star Alliance, the worlds first alliance, members of MileagePlus have access to several airlines worldwide.