The euro (EUR or €) is the single currency for the European Union and currently 13 of its member states. The euro was formally established as a unit of exchange on 1 January 1999, and euro banknotes and coins (see euro coins) entered circulation in 12 member states on 1 January 2002.

On 1 January 2007 Slovenia, a state that joined the EU in May 2004, became the 13th state to join the euro area. The remaining EU states with the exception of the United Kingdom and Denmark are required to adopt the euro after meeting the necessary economic conditions to enter the eurozone.

There are seven different denominations, each having a distinctive colour and size. The design for each of them has a common theme of European architecture in various artistic periods. The front (or recto) of the note features windows or gateways while the back (or verso) has bridges.

Care has been taken so that the architectural examples do not represent any actual existing monument, so as not to induce jealousy and controversy in the choice of which monument should be depicted

Common to all notes are the European flag, the initials of the European Central Bank in five versions (BCE, ECB, EZB, ???, EKP), a map of Europe on the back, the name "euro" in both Latin and Greek script and the signature of the current president of the ECB. The 12 stars from the European Flag are also incorporated into every note.

The euro banknote designs were chosen from 44 proposals in a design competition, launched by The Council of the European Monetary Institute (EMI) on 12 February 1996. The winning entry, created by Robert Kalina from the Oesterreichische Nationalbank, was selected on 3 December 1996.

The paper used for euro banknotes is 100% pure cotton fibre, which improves their durability as well as imparting a distinctive feel.

The following member overseas territories are shown: the Azores, French Guiana, Guadeloupe, Madeira, Martinique, Réunion, and the Canary Islands. Cyprus and Malta are not shown, as they only joined the EU in 2004; also Malta is too small to be shown, with the minimum size for depiction being 400km².

These designs use the Duisenberg signature, which has since been replaced by the signature of Jean-Claude Trichet, the present president of the ECB.
5 €
Size: 120 x 62 mm
Color: Gray
Design: Architecture Classical
10 €
Size: 127 x 67 mm
Color: Red
Design: Architecture Romanesque
20 €
Size: 133 x 72 mm
Color: Blue
Design: Architecture Gothic
50 €
Size: 140 x 77 mm
Color: Orange
Design: Architecture Renaissance
100 €
Size: 147 x 82 mm
Color: Green
Design: Architecture Baroque & Rococo
200 €
Size: 153 x 82 mm
Color: Yellow
Design: Art Nouveau
500 €
Size: 160 x 82 mm
Color: Purple
Design: Modern 20th century

Source: Wikipedia