BBC News Online tells you some of the stories behind the single currency. Click on the links at the top of the page to find out more.
Since January 2002, euro notes and coins are a fact of life for more than 300 million people across the 12-country eurozone. During the next five to eight years, this will grow to up to 475 million people as 10 more countries join the European Union.
All these people need a lot of notes and coins. Just to meet the current eurozone's needs, more than 15 billion bank notes and 50 billion coins were printed and minted.
And surprisingly, the launch of the euro as a cash currency went very smoothly. The doomsday scenarios about mass robberies, fraud schemes, giant queues at cash registers and other worries about wholesale confusion and chaos never came true.
But there were problems too. Many companies across the eurozone were accused of profiteering, trying to slip in hefty price rises during the changeover.