Guto Thomas BBC Wales Europe correspondent

The EU will contain 25 countries from Saturday

But who are these new countries? And what will the effect of enlargement be for Wales?

The EU has developed dramatically since it began in the early 1950s as a group of six, concentraing purely on economic matters.

1 May 2004 is therefore an historical date, when Europe will see its borders expanded to its largest ever size - and it will do so through the consent of the people of Europe.

Jan Royall, the European Commission's Representative in Wales says that bringing 25 countries, with over 450 million citizens, under the safe roof should be a moment for mature reflection.

"I think people bandy the term historic about but actually this truly is a historic event.

"For the first time Europe is being reunited peacefully.

It creates lots of opportunities for business, for individuals, for students, for charitable organisations Dr Roger Scully

"It's being reunited using the force of argument rather than the force of arms

"This is good news for Wales - it brings us peace, prosperity, stability, jobs."

Most of the 10 new countries are from the East - the old Warsaw Pact countries, such as Poland and Hungary, as well as those such as Latvia and Estonia who won their independence after the fall of communism in the Soviet Union.

During a short speech on enlargement in Westminster this week, observers noted that Plaid Cymru's President Dafydd Iwan, could hardly contain his envy - particularly since six members of the new European Union are as small if not smaller than Wales, but they will all have more MEPs.

However, enlargement does offer all kinds of opportunities for Wales, according to Dr Roger Scully, the Director of the Centre for European Studies at the University of Wales, Aberystwyth.

"It creates a larger market, it creates more opportunities for travel, and for work in other parts of Europe.

Population to MEP ratio Malta - 0.4m people: 5 MEPs Luxembourg - 0.4m: 6 Cyprus - 0.8m: 6 Estonia - 1.4m: 6 Slovenia - 2.0m: 7 WALES - 2.2m: 4 Latvia - 2.4m: 9

"It creates lots of opportunities for business, for individuals, for students, for charitable organisations.

"For almost you name it, it has a potential impact."

Perhaps more than anything, enlargement is about jobs and opportunities.

There will be more consumers in the enlarged EU market to buy goods, but that also means more competition for Welsh producers and manufacturers.

But, according to the First Minister, Rhodri Morgan, this . shouldn't necessarily be seen as a threat.

"I think there are big opportunities for Wales as well, because of what we already know about how to create new jobs . . . we can help those countries, and in doing that, we can help ourselves."

For Welsh jobs, for the economy, for agriculture and exports, for regional funding, and for fundamental rights such as the freedom of movement and migration, European Enlargement is now almost a reality.

And with more countries queuing up to join, then the implications for Wales could be enormous.