The euro is the official currency of 19 European Union countries which collectively make up the euro area, also known as the eurozone.
Some EU countries have yet to meet the criteria required to join the euro area while Denmark has opted not to participate.
Within the euro area, the euro is the only legal tender. In the absence of a specific agreement concerning the means of payment, creditors are obliged to accept payment in euros.
Parties may also agree to transactions using other official foreign currencies (e.g. the US dollar). They may also agree to use privately issued ‘money’ like local exchange trading systems (e.g. voucher-based payment systems) or virtual currencies (e.g. Bitcoin).
These private and business transactions are still subject to taxation law, business law, anti-money laundering law and other general commodity trade rules. However, currencies which are not official within the euro area, are not governed by monetary law.