The euro is the most significant achievement of European monetary reform since the Roman Empire. The euro not only makes the European single market more perfect, but also facilitates the free trade among the countries in the euro zone, which is an important part of the EU integration process.

Although Monaco, San Marino and Vatican are not EU countries, they used to use French francs or Italian lira as their currencies, and they also used euros, and authorized to mint a small number of their own euro coins. Some non-EU countries and regions, such as Montenegro, Kosovo and Andorra, also use the euro as a payment tool. ?