Passengers have passed through Dublin Airport's Terminal 2 as the new 600 million euro project was officially opened.
Aer Lingus operated the inaugural flight from Manchester as Taoiseach Brian Cowen formally unveiled the new three-storey facility.
Mr Cowen said: "T2 was designed and built not just for this year or the next, but for many decades into the future. To view it through the prism of the current downturn would be short-sighted in the extreme.
"By investing prudently in improved facilities, we are laying the foundations for future growth and prosperity; not just for Dublin Airport, but also for the wider Irish economy."
Construction on the new building began in October 2007 and, at its peak, employed up to 2,600 workers on site, with 1,000 new jobs created with the building's opening.
T2 will be home to Aer Lingus, American Airlines, Continental Airlines, Delta Air Lines, Etihad Airways and US Airways. It will open on a phased basis.
Aer Lingus will have transferred all its services to the new facility by January and has asked all passengers to come to Terminal 1 for advice on where to go. Etihad will start operating its services from Tuesday.
T2 will also house a new US pre-clearance facility allowing passengers on US-bound flights to clear all customs, immigration, agriculture and security checks before leaving Ireland. US carriers will transfer when the pre-clearance facility opens in the New Year.
Online travel agency GoHop.ie said people were confused over the new travel arrangements.
Founder Stephen McKenna said: "The situation in relation to US customs and immigration needs to be clarified further and implemented as soon as possible before people can enjoy the real benefits of this new terminal."