Title: Economy of Europe
Content:  The most common currency within Europe is the Euro (€), the currency of the European Union. To join, each new EU member must meet certain criteria, when these are met their own currencies will be replaced by the euro. Becoming a member of the EU involves a pledge to work towards Eurozone membership, (except in the case of Denmark, which has an opt-out). Currently, 19 of the 27 EU member states use the euro. Each EU member's central bank is part of the European System of Central Banks, and in addition, those that use the euro are part of the European Union's central bank, the European Central Bank. There are some non-EU members who have elected to use the euro as their national currency like Kosovo and Montenegro, either with or without specific agreements with 
Title: List of currencies in Europe
Content:   There are 25 currencies currently used in the 50 countries of Europe, all of which are members of the United Nations, except Vatican City, which is an observer. All de facto present currencies in Europe, and an incomplete list of the preceding currency, are listed here. A currency is a medium of exchange, such as money, banknotes, and coins. In Europe, the most commonly used currency is the euro (used by 25 countries); any country entering the European Union (EU) is expected to join the eurozone when they meet the five convergence criteria. Denmark is the only EU member state which has been granted an exemption from using 
Title: Currencies of the European Union
Content:  The euro is the result of the European Union's project for economic and monetary union that came fully into being on 1 January 2002 and it is now the currency used by the majority of the European Union's member states, with all but Denmark bound to adopt it. It is the currency used by the institutions of the European Union and in the failed treaty on a European Constitution it was to be included with the symbols of Europe as the formal currency of the European Union. The euro is also widely used by other states outside the EU. Except for the one state with 
Title: Euro
Content:  The euro (symbol: €; code: EUR) is the official currency of 19 of the member states of the European Union. This group of states is known as the eurozone or euro area and includes about 343 million citizens. The euro, which is divided into 100 cents, is the second-largest and second-most traded currency in the foreign exchange market after the United States dollar. The currency is also used officially by the institutions of the European Union, by four European microstates that are not EU members, the British Overseas Territory of Akrotiri and Dhekelia, as well as unilaterally by Montenegro and Kosovo. Outside Europe, a number of special territories of 
Title: Economic history of Europe (1000 AD–present)
Content:  The Euro became the official currency of certain European Union members on January 1, 2001. The currency was signed into effect in 1992 in the Treaty of Maastricht. The initial idea behind the Euro was that it eliminates exchange rates between European nations and makes currency fluctuation risks minimal.
Title: Symbols of the European Union
Content:   The euro, €, was not one of the original symbols created by the Council of Europe and is specific to the EU, but it has become a symbol since it replaced 12 national currencies in 2002. It is now used by most EU Member States and hence it (along with its currency symbol) has become one of the most tangible symbols of European unity for citizens of the European Union (though this of course is not intended to apply to wider Europe as the others do).
Title: Currencies of the European Union
Content:  There are nine currencies of the European Union used officially by member states. The euro accounts for the majority of the member states with the remainder operating independent monetary policies. Those European Union states that have adopted it are known as the eurozone and share the European Central Bank (ECB). The ECB and the national central banks of all EU countries, including those who operate an independent currency, are part of the European System of Central Banks.
Title: European Currency Unit
Content:  The European Currency Unit (Unité de compte européenne, Europäische Währungseinheit; ₠, ECU, or XEU) was a unit of account used by the European Economic Community and composed of a basket of member country currencies. The ECU came in to operation on 13 March 1979, and was assigned the ISO 4217 code. The ECU replaced the European Unit of Account (EUA) at parity in 1979, and it was later replaced by the euro (EUR) at parity on 1 January 1999. As a unit of account, the ECU was not a circulating currency, and did not replace or override the value of the currency of EEC member countries. However, it was used to price some international financial transactions and capital transfers.
Title: Currency union
Content:  The European currency union is a part of the Economic and Monetary Union of the European Union (EMU). EMU was formed during the second half of the 20th century after historic agreements, such as Treaty of Paris (1951), Maastricht Treaty (1992). In 2002, the euro, a single European currency, was adopted by 12 member states. Currently, the so-called Eurozone has 19 member states. The other members of the European Union are required to adopt the euro as their currency (except for Denmark, which has been given the right to opt out), but there has not been a specific date set. The main independent institution responsible for stability of the euro is the European Central Bank (ECB). Together with 15 national banks it forms the European System of Central Banks. The Governing Board consists of the Executive Committee of the ECB and the governors of individual national banks, and determines the monetary policy, as well as short-term monetary objectives, key interest rates and the extent of monetary reserves.
Title: Euro sign
Content:  The euro sign, €, is the currency sign used for the euro, the official currency of the eurozone and some other countries (such as Kosovo and Montenegro). The design was presented to the public by the European Commission on 12 December 1996. It consists of a stylized letter E (or epsilon), crossed by two lines instead of one. In English, the sign immediately precedes the value (for instance, €10); in most other European languages, it follows the value, usually but not always with an intervening space (for instance, 10€, 10€).

Question: what is the name given to the common currency to the european union?
Answer: euro.
The euro.