The European Union has opened the way to the admission of 10 new member-states in 2004 after two days of wrangling with the candidate countries over the details of how to finance their accession.
In Copenhagen last night, the Taoiseach, Mr Ahern, said the deal marked "a quantum leap" towards European unity.
"The positive influence to the enlargement process given by our Nice referendum result last October has been realised here today. And I am happy to say that it will fall to Ireland, as Presidency, to formally welcome the new member-states in 2004," he said.
The agreement means that Poland, the Czech Republic, Hungary, Slovakia, Slovenia, Estonia, Lithuania, Latvia, Cyprus and Malta will join the EU in May 2004.
In a joint declaration, leaders of the 15 member-states and the 10 countries that will join in 2004 described the agreement as a great moment for Europe.
"Our common wish is to make Europe a continent of democracy, freedom, peace and progress. The Union will remain determined to avoid new dividing lines in Europe and to promote stability and prosperity within and beyond the new borders of the Union.
"We are looking forward to working together in our joint endeavour to accomplish these goals," the leaders said.
In the end, the candidate countries received little more than the €40 billion financial package the EU proposed when the summit began. But Poland secured a special deal that allows it to use €1 billion originally designated as structural funds to solve a potential cash flow problem in 2005. The redesignation means that Warsaw will not only be able to use the money two years earlier than planned but will have fewer restrictions on how to spend it. The move will save Poland a further €250 million it would have had to spend "co-financing" the structural funds.
Other candidate countries will share an extra €300 million on top of the EU's original financial package.
Addressing EU leaders and their counterparts from the candidate countries after the summit, the Danish prime minister, Mr Anders Fogh Rasmussen, said they had fulfilled the ambition of generations of Europeans. "Europe is spreading its wings in freedom, in prosperity and in peace. This is a truly proud day for Europe. It is a triumph for liberty and democracy. To our new members I say warmly, welcome to our European family. Our new Europe is born," he said.
Commission President, Mr Romano Prodi, said enlargement had been his priority since assuming office three years ago. He said last night's decision would bring to an end the divisions in Europe.
"For the first time in history Europe will become one because unification is the free will of its people. The European Union has stood by its commitments. The deal that we have reached here in Copenhagen represents the EU at its best: leadership, solidarity and determination," he said.
The EU leaders agreed that Romania and Bulgaria can expect to join the EU in 2007. And they told Turkey that, if it fulfils the political conditions for EU membership by December 2004, it can start accession negotiations without delay.