Ireland put on its warmest face to greet the leaders of the 10 countries that have joined the EU after a wait of nearly 15 years.
By William Horsley
In bright sunshine they smiled for a family photo - the first ever of all 25 leaders as full EU members.
Children from every one of those countries came forward and shyly presented each of the 25 national flags to each of the leaders.
Wide smiles greet the leaders of the new EU members
As the flags were raised and fluttered together in the wind, a choir sang the EU's anthem, Beethoven's Ode to Joy.
Surrounded by the lush green lawns and magnificent trees of Dublin's Phoenix Park, the leaders did look, while the ceremony went on, like members of a large and happy family.
The Irish did it all with traditional Celtic charm. The Nobel prize-winning Irish poet, Seamus Heaney, read out a poem, composed for the occasion, called Beacons at Bealtaine.
It included the lines: "So on a day when newcomers appear/ Let it be a homecoming..."
The Irish hosts explained that Bealtaine, the old Irish name for May Day, is traditionally known as the Celtic feast of the first day of summer, and the day when the first magical inhabitants of Ireland arrived on the island.
It may be seen as auspicious that the formal accession of the new EU members has taken place on this day.
The Irish Prime Minister, Bertie Ahern, said of the newcomers: "We welcome them with pride. We welcome them with hope."
He hopes to bind the enlarged EU together with another sort of charm - his gift to his fellow heads of state and governments was a pair of Irish silver wine bottle coasters, finished with a Celtic knot which symbolises eternity.
The mood of celebration was infectious. Dublin was drenched in summer sun, which brought tens of thousands of visitors out to the European Fair in the city centre.
They soaked up the culture, food and drink, and sights and sounds of all the 25 EU countries, as well as Romania, Bulgaria and Turkey, which expect to be next in line to join the club.
Dubliners are swept along with EU fever
For once, politics was meant to be put on one side. But still the leaders sent out some messages on the Day of Accession which point to some vigorous arguments within this "European family".
Romano Prodi, the European Commission president, told a news conference that all EU states must set aside their national interest and abide by policies decided by majority voting in future.
The newcomers from the east are not so sure about that.
Poland's President, Alexander Kwasniewski, said before coming here that he did not want to see the large, western countries in Europe forming an "exclusive" club against the interests of the new members.
The Prime Minister of Estonia, Johan Parts, said the EU must be a union of nations, all of them equal, not just on paper but in reality.
Next time they meet, the EU family will put their expressions of goodwill to the test.
At the next scheduled EU summit, in Brussels in June, they will try again to reach agreement on the balance of power and the policies of the future EU, in a legally-binding European constitution.