This paper shall investigate the trade integration between Turkey and the EU. The plan of the book is as follows. At first the historical background of the development concerning the trade relations between the two parties is conveyed. This includes the period from first association to implementing a customs union (CU) between Turkey and the European Union (EU) and to deeper integration abolishing barriers of trade until today.Subsequently an evaluation of the influence of the customs union follows in chapter 3 which constitutes the main part of the paper. Hereby the analysis is divided into the short-term static and long-term dynamic effects of the CU with the EU that Turkey entered on 1st January 1996. To analyze the static effects this paper adopts Viner's traditional approach, by comparing the trade creation effects with the trade diversion effects resulting from the removal of trade restrictions for Turkey and the EU as a whole. Thus, the predominant economical theory applied in this paper is the neoclassical customs union theory. This theory was chosen because it still is the predominant and widely recognized theory in analyzing trade data providing a variety of tools. Within the neoclassical theory Ricardo as well as Heckscher-Ohlin play an important role as a tool of analysis. In the relevant passages in the text the most important theoretical principles will be explained with the help of the Turkish example. At the limits of the neoclassical theories the new trade theory is supposed to help out especially where the assumptions of the neoclassical theory limit further analysis.It is the purpose of this paper to analyze the question how the trade liberalization in form of the CU between Turkey and the EU influences the development of Turkish welfare, specialization in different sectors, economies of scale, competitiveness, technological transfer and direct foreign investment. In some parts of the paper the analysis also refers to some effects for the EU, but main emphasis shall clearly be laid upon the effects on the Turkish economy. For the analysis foreign trade data is used which was compiled by the Turkish Undersecretariat of the Prime Ministry for Foreign Trade, the Prime Ministry Undersecretariat of Treasury, the Turkish Statistical Institute and Eurostat. The analysis concentrates on the development within the last years, because not many studies were written in the 21st century or using data from this period. The last subitem within chapter 3 allows a glance at the possibility of further integration taking monetary integration as an example. Last but not least chapter 4 will summarize the findings of the previous sections which will lead to a final estimation of the effects of the CU on Turkey and the EU.