The euro (sign: €; code: EUR) is the official currency of the Eurozone: 16 of the 27 Member States of the European Union (EU). It is also the currency used by the EU institutions. The eurozone consists of Austria, Belgium, Cyprus, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Malta, the Netherlands, Portugal, Slovakia, Slovenia and Spain. Estonia is due to join the eurozone on 1 January 2011. The currency is also used in a further five European countries, with and without formal agreements, and is consequently used daily by some 327 million Europeans. Over 175 million people worldwide use currencies which are pegged to the euro, including more than 150 million people in Africa.

The euro is the second largest reserve currency (a status it inherited from the German mark) as well as the second most traded currency in the world after the U.S. dollar. As of June 2010[update], with more than €800 billion in circulation, the euro is the currency with the highest combined value of banknotes and coins in circulation in the world, having surpassed the U.S. dollar.[note 15] Based on IMF estimates of 2008 GDP and purchasing power parity among the various currencies, the eurozone is the second largest economy in the world.

The name euro was officially adopted on 16 December 1995. The euro was introduced to world financial markets as an accounting currency on 1 January 1999, replacing the former European Currency Unit (ECU) at a ratio of 1:1. Euro coins and banknotes entered circulation on 1 January 2002.

The euro is managed and administered by the Frankfurt-based European Central Bank (ECB) and the Eurosystem (composed of the central banks of the eurozone countries). As an independent central bank, the ECB has sole authority to set monetary policy. The Eurosystem participates in the printing, minting and distribution of notes and coins in all Member States, and the operation of the eurozone payment systems.

The 1992 Maastricht Treaty obliges most EU Member States to adopt the euro upon meeting certain monetary and budgetary requirements, although not all states have done so. The United Kingdom and Denmark negotiated exemptions, while Sweden turned down the euro in a 2003 referendum, and has circumvented the obligation to adopt the euro by not meeting the monetary and budgetary requirements. All nations that have joined the EU since 1993 have pledged to adopt the euro in due course.

The euro is divided into 100 cents (sometimes referred to as euro-cents, especially when distinguishing them from other currencies). In Community legislative acts the plural forms of euro and cent are spelled without the s, notwithstanding normal English usage. Otherwise, normal English plurals are recommended and used; with many local variations such as 'centime' in France.

All circulating coins have a common side showing the denomination or value, and a map in the background. For the denominations except the 1-, 2- and 5-cent coins that map only showed the 15 Member States which were members when the euro was introduced. Beginning in 2007 or 2008 (depending on the country) the old map is being replaced by a map of Europe also showing countries outside the Union like Norway. The 1-, 2- and 5-cent coins, however, keep their old design, showing a geographical map of Europe with the 15 Member States of 2002 raised somewhat above the rest of the map. All common sides were designed by Luc Luycx. The coins also have a national side showing an image specifically chosen by the country that issued the coin. Euro coins from any Member State may be freely used in any nation which has adopted the euro.

The coins are issued in €2, €1, 50c, 20c, 10c, 5c, 2c, and 1c denominations. In order to avoid the use of the two smallest coins, some cash transactions are rounded to the nearest five cents in the Netherlands (by voluntary agreement) and in Finland (by law). This practice is discouraged by the Commission, as is the habit of certain shops to refuse to accept high value euro notes.

Commemorative coins with €2 face value have been issued with changes to the design of the national side of the coin. These include both commonly issued coins, such as the €2 commemorative coin for the fiftieth anniversary of the signing of the Treaty of Rome, and nationally issued coins, such as the coin to commemorate the 2004 Summer Olympics issued by Greece. These coins are legal tender throughout the eurozone. Collector's coins with various other denominations have been issued as well, but these are not intended for general circulation, and they are legal tender only in the Member State that issued them.

The design for the euro banknotes have common designs on both sides. The design was created by the Austrian designer Robert Kalina. Notes are issued in €500, €200, €100, €50, €20, €10, €5. Each banknote has its own colour and is dedicated to an artistic period of European architecture. The front of the note features windows or gateways while the back has bridges. While the designs are supposed to be devoid of any identifiable characteristics, the initial designs by Robert Kalina were of specific bridges, including the Rialto and the Pont de Neuilly, and were subsequently rendered more generic; the final designs still bear very close similarities to their specific prototypes; thus they are not truly generic. Some of the highest denominations such as the €500 are not issued in all countries, though they remain legal tender throughout the eurozone.