The European Union Customs Union
The European Union Customs Union (EUCU) is a customs union which consists of all the member states of the European Union (EU) and a number of surrounding countries.
The customs union is a principal task of the European Economic Community, established in 1958, and now succeeded by the European Union. No customs are levied on goods travelling within the customs union and—unlike a free trade area—members of the customs union impose a common external tariff on all goods entering the union. One of the consequences of the customs union is that the European Union has to negotiate as a single entity in international trade deals such as the World Trade Organisation.
Non-EU members 
EU applicant Turkey and two bordering microstates—Andorra and San Marino — are in customs union with the EU. Monaco, while not a member of the EU, is part of the EU customs territory through an agreement with France.
While all EU members are part of the customs union, not all of their respective territories form part of the customs union. This may be because a territory is not part of the EU, because the territories have opt-outs, or are excluded from the customs union because of their economic or geographic circumstances; see Special member state territories and the European Union.
See also