The euro was three years old before anyone could touch it.
On 1 January 1999 the euro was introduced in eleven countries as book money: accounts, transfers and stock prices ran in euros while people still held Deutsche Marks or pesetas. Notes and coins arrived only on 1 January 2002 in twelve states. Within a few weeks the old currencies were out of circulation.
Useful: The biggest cash changeover in history, done in under two months.
Source: de.wikipedia.org