A customs union is a stage of multinational integration, during which the member states agree, by treaty, to refrain from imposing any customs duties, charges having equivalent effect or quantitative restrictions on each other and to adopt an external common customs tariff in their relations with third countries. The common customs tariff implies not only a common customs policy but also a common foreign trade policy [see chapter 23]. Furthermore, the freedom of movement is applicable in a customs union regardless of the origin of goods, thus eliminating customs controls at internal borders.

The founders of the European Economic Community had, from the start, the goal not only of setting up a customs union, but also a common market in which goods, services and capital could be traded freely. In economic integration, they foresaw not only a formula offering economic advantages but also the means to set up the conditions for political union in Europe. In order to achieve this, a sound foundation was required. Customs union was, accurately enough, such a foundation; it allowed for unprecedented trade growth in the participating Member States and the construction upon it of the entire European edifice. In fact, all the common policies examined in this book would be unthinkable were they not based on a customs union.