The European Union (EU) is the largest trading block in the world, occupying an important position in the world's trading in goods and services. It is a major actor in international trade diplomacy. As an important part of a country's economic policies, external foreign trade policy plays a crucial role in the economic activity through tariffs and non-tariff barriers. This dissertation will discuss and explore how the EU, as an economic power and independent participant in the international trade system, handles both cooperative and conflictive international trade activities with the United States (U.S.). It first focuses on exploring the EU external trade policy, including its decision-making mechanism and negotiation channels. Subsequently, it focuses on the characteristics of the EU's trade policy framework and its international status in the world trade, and the EU's trade policy within the WTO context under the Doha Development Agenda. As an economic power and significant trade actor, the EU as a singular actor interacts with the U.S., especially in the dimension of bilateral trade relations. The method of case study is applied to explore the trade relations between the EU and the U.S., so as to further reflect the independence of the EU as an international trade entity. It uses two cases-transatlantic economic integration and the banana trade friction-to study the different characteristics of the trade relationship between the EU and the U.S.: one cooperative and the other competitive. The thesis concludes by summarizing the characteristic of the EU external trade policy and their influence upon the EU trading system. Key Words: European Union; trade actor; the common commercial policy; trade relations; the United States.