Getting ready for the euro has been a huge task, from minting coins to changing cash machines

(CNN) -- Say goodbye to the German mark, French franc, Spanish peseta, Italian lira and eight other European currencies.

All 12 have disappeared, replaced by the euro -- the most significant new currency to hit world markets since the dollar.

It's the biggest currency conversion ever undertaken on the continent, and it's driven by European integration and the hope of greater economic prosperity.

"It will mean, of course, that you can go from one country to another -- just as you can go from one state to another in the United States -- and not have to worry about changing money and the cost of changing money," says Richard Portes of the London Business School.

"But it also means you've got one single market with one currency stretching from Finland down to Spain, so manufacturers are pricing for a single market so that people can compare pricing."

The attraction is simplicity and efficiency.

The euro has existed as a convenient accounting currency for years: European stocks have been priced in euros, currency traders have bought and sold euros, and the exchange rates for most participating currencies against the euro were fixed in January 1999.

What came in January 2002 was the real, money-in-your-hands euro.

It was a huge task: 50 billion coins were minted, 14.5 billion notes were printed, and 3.5 million vending machines had to be adapted.

"First of all you have to have a plan to change all of the cash points and cash machines for train tickets, etc.," says European financial affairs adviser Graham Bishop. "Then you have to be able to deliver it, of course; you have to have printed and minted the notes and coins beforehand."

Aside from the practical difficulties, there were the political complications: Of the 15 European Union members, three -- Britain, Denmark and Sweden -- are not participating in the euro primarily because of public opinion against the new currency.

But they do have the option to join at a later stage, as do the many EU applicants.

"We have 15 member states, and therefore the euro could conceivably extend to the 15," says Roberto Leonardi of the London School of Economics. "When we have enlargement after 2004, there is the prospect of 11 additional countries coming in, so therefore you could have the adoption of the euro in 26 countries.

"That is a major economic market. It would be a lot larger than the United States, so what we are talking about is the creation of the next major world currency."

Potentially the euro could become the currency of half a billion people, and what all countries must remember is that now notes and coins have been issued, realistically there's no going back.

For richer for poorer, weaker or stronger the euro is here to stay.