After a glass or two of champagne and a good night's sleep to celebrate agreeing a historic constitution for the European Union, the bloc's leaders now start the tough job of persuading their people to ratify it.
They also need to find a new president of the EU's executive Commission, a task which has already exposed lingering divisions between member states over the US-led war in Iraq and deep-seated differences in their vision of European integration.
The constitution will give the bloc stronger leadership with a long-term president of the European Council and a foreign minister to represent it on the world stage, more powers for the European Parliament and more decisions taken by majority vote.
It is also meant to make the bloc's complex and remote institutions easier for citizens to understand.
"This is a fundamental advance for the European Union," said the Taoiseach, Mr Ahern, who resurrected negotiations that collapsed last December under the Italian presidency
and steered them to success through Dublin's six-month presidency.
"This is a win-win solution which is what we set out months ago to achieve," he said shortly before midnight after a tense, two-day summit.
But all 25 member states still have to ratify the treaty before it can take effect, some by a vote in national parliaments and some by referendum.
EU officials, mindful of the dismal record of most member states in effectively explaining the bloc to their voters, are already urging them to remedy this before ratification.
"We've now adopted the constitutional treaty politically, the time starts now to explain it to the public, to sell it and to ratify it," outgoing European parliament President Mr Pat Cox said as the summit wound up.
The next task facing the bloc's leaders, however, is to select a successor to Italian Mr Romano Prodi as president of the European Commission from November.
There were two favourites for the job during the summit: Belgian Prime Minister Mr Guy Verhofstadt, backed by France and Germany but anathema to Britain, and EU External Relations Commissioner Mr Chris Patten, who was out of the question for Paris.
No clear front-runner was left in the frame after the meeting and some diplomats said Mr Ahern himself might win broad support, although he has denied any interest in the post.
Mr Ahern said he was determined to resolve the vexed question before the end of Ireland's presidency: that gives him less than two weeks.