The Abu Dhabi-based airline has ordered 35 Boeing 787 Dreamliner aircraft and 10 777-300ER.
The carrier has also agreed options for a further 25 Dreamliners and 10 777s with the US manufacturer, and purchasing rights for an additional 10 787s and another five 777s.
If all these rights are exercised, the value of the deal could exceed $20bn.
Etihad’s 787 planes will be delivered between 2015 and 2020. The 777s will begin to arrive in Abu Dhabi from 2011.
The deal was signed on 14 July, on the first day of the Farnborough International Airshow in the UK.
Etihad chief executive officer James Hogan says that despite the severe pressure being placed on airlines by rising fuel prices, the scale of the order reflected the company’s confidence in the Abu Dhabi government’s projects to promote and invest in the emirate, and of Etihad’s pivotal role in that scheme.