A Customs Union is a union of states, which share a common customs area. However, there is not a standard type of custom union. A customs union may be built according to different forms and for different legal reasons. Turkey signed a Customs Union agreement with the European Union in 1995. The customs union with Turkey is a good example of a country not yet a member of the EU, but with which the EU has a customs union. The customs union between Turkey and the EU concerns industrial and processed agricultural products. It is of great importance for Turkey to dismantle customs duties and similar fees. Turkey has put the common external tariff of the EU standard into practice against third countries. However, on the Turkish side in particular, there were economic concerns and criticism. On the other side there are also proponents of the customs union in Turkey. In this paper we examine the meaning and background of the customs union and the taxation in international trade.