The euro was launched on January 1, 1999, at first only for accounting and financial transactions, and then three years later as notes and coins.
Here is a recap of defining moments for the currency, which was envisaged in the European Union's Maastricht Treaty:
On December 31, 1998, on the eve of the euro launch, the definitive conversion rates are revealed by the new European Central Bank: one euro will buy 1.95583 Deutschmarks, 6.55957 French francs and 1,936.27 Italian lire.
Tens of thousands of people in banks and European stock exchanges get to work over the New Year break to ensure everything is ready when financial markets reopen on January 4.
Shops that displayed prices in both currencies with approximate exchange rates update their tags.
On January 1, 1999 the euro becomes the official currency for 291 million people in 11 countries: Austria, Belgium, Finland, France, Germany, Ireland, Italy, Luxembourg, The Netherlands, Portugal and Spain.
The new money can be used for bank transfers along with payments by cheque, traveller's cheque and bank card.
Monday, January 4 is the euro's baptism on foreign exchange markets. One euro initially trades for more than $1.18. But weeks later it slides to less than a dollar and at the end of October it hits its lowest rate ever, at $0.8230.
On January 1, 2001 Greece becomes the 12th country to adopt the single currency.
Coins and notes
On January 1, 2002 the euro becomes physical legal tender as some 15 billion notes and more than 50 billion coins are put into circulation, shaking up the lives of 304 million Europeans.
People familiarise themselves with the single currency, sometimes using pocket calculators to make it easier to work out conversions.
Unlike most currencies, the euro notes show no national symbols, opting instead for bridges and windows.
A period of two legal tenders being in circulation in each country begins as the national currencies are gradually phased out, lasting until March 1.
On July 15 the euro reaches parity with the dollar again.
In 2003 Sweden, in a referendum, joins Denmark and Britain in rejecting the single currency.
Elsewhere, new EU member countries adopt the single currency: Slovenia in 2007, Cyprus and Malta in 2008, Slovakia in 2009, Estonia in 2011, Latvia in 2014 and Lithuania in 2015.
On July 15, 2008 the euro reaches an exchange rate high, trading at $1.6038 as the US is rocked by the sub-prime mortgage crisis. That November, however, the euro zone enters a recession lasting a year.
In 2010 the EU is mired in a debt crisis. In May the EU and International Monetary Fund (IMF) provide a €110-billion bailout for Greece, which in turn commits to a severe austerity plan. A month later the euro plunges below $1.20.
In November, Ireland, where banks are crippled by debt, also obtains an EU-IMF bailout plan of €85 billion.
Portugal obtains a €78-billion bailout in May 2011.
Saving the euro
On July 25, 2012 Spain's long-term interest rate soars above 7.6%, sparking fears of a euro collapse.
A day later European Central Bank chief Mario Draghi promises to do "whatever it takes to preserve the euro".
In August, in one week, the ECB buys back bonds of euro zone nations worth €22 billion to support Italy and Spain.
The EU agrees in October to cancel a part of the Greek debt and to extend a new set of loans.
In May 2014 the single currency rises near $1.40, hitting exports. Then months later it comes close to $1.05 in a slide that is linked to the buying of assets by the ECB to support the economy.
In July the next year Greece obtains a third bailout aimed at keeping it from crashing out of the eurozone, or "Grexit".
'Bin Laden' banknotes
In 2016 the ECB says it plans to stop issuing the €500 note by the end of 2018.
The banknote is known as the "Bin Laden" and believed to be favoured by criminals for money laundering and terrorist financing.