The most commonly used currency in the European Union is the euro (€). The euro was introduced in 1999 for electronic transactions and became physical currency in 2002, following the establishment of the Eurozone. It is used by 19 of the 27 EU member states, collectively known as the Eurozone, making it the second most widely held currency in the world. The euro facilitates trade, travel, and economic stability within Europe, helping to strengthen economic ties among participating countries.