On this day in 2002, 12 of the 15 countries that then formed the European Union officially adopted the euro as their currency – the largest single monetary changeover in history.

Of all the EU countries only Sweden (which rejected the adoption of the euro by referendum) and the UK and Denmark (which negotiated exemptions) did not switch to the new currency.

Established by the Maastricht Treaty in 1992, the euro had been in use as a non-cash currency (in banking transitions etc) since January 1, 1999. But January 1, 2002 was the day on which banknotes and coins were fed out across the continent.

[Read more: February 15, 1971 - Britain switches to decimal currency]

Seven banknotes and eight coins were issued for the launch. The notes shared the same design across all countries in the euro area, while the coins have a common design on one side and a country-specific design on the other.

Most member countries allowed their old currencies to remain as legal tender for another two months, with the exception of Germany, where the Deutschmark could no longer be used after December 31, 2001.  However, banknotes and coins in old currencies remained exchangeable at banks for varying amounts of time.

Monetary policy became the responsibility of the independent European Central Bank (ECB) and the national central banks of the countries which adopted the euro. Member states remained responsible for their own fiscal policy.

[Read more: November 12, 1984 - End of the road for the pound note]

The introduction of the euro was largely deemed a success. Within five days, more than half of all cash transactions in the eurozone were being made in the new currency, and since the end of 2002 it has traded above the US dollar.