The euro began as an accounting currency for participating European Union countries in 1999.
On 1 January 1999, the euro was introduced for electronic payments, financial transactions, and official accounting in the countries that formed the initial euro area. National currencies continued circulating as physical money during a transitional period, while exchange rates between them and the euro were fixed irrevocably.
Euro banknotes and coins entered public circulation on 1 January 2002, replacing national cash in participating countries. This distinction explains why 1999 and 2002 are both important dates in euro history. The currency is issued by the European Central Bank and national central banks of euro-area members. Denmark and the United Kingdom secured opt-outs, while several other EU members were expected to adopt the euro after meeting required conditions.