歐盟經濟整合已趨成熟，其對於國際政治經濟有著相當影響力。在全球化與貿易自由化的潮流下，第三國與歐盟之交往愈形密切，常常需要透過國際談判來達成協議。歐盟乃一區域整合體，內部包含十五國之共同利益，會員國透過制度達成協議，以利進行對外貿易談判。其主要對外貿易政策之負責機構為：歐盟理事會及執委會，執委會雖為代表歐盟對外談判者，但仍受到理事會之掣肘。理事會對外決策係透過投票制度呈現，而歐盟整合至今，理事會所演變之投票制亦有所改變，從一致決至多數決，在不同投票制度下，所賦予談判代表對外權力與議價區自然有然有所區別，並影響最後國際協議達成與否。理解此種制度面呈現之特性，方能作為與歐盟在國際貿易談判交涉之基礎。

　　　　　Now representing its 15 member states in international trade negotiations. It will be beneficial to third countries in their trade talks with the EU if they have deeper insight into how the EU forms its position at home. This paper aims to contribute to this goal. Examing the voting systems suggest the different weights the Council and commission hold in deciding the EU's external relations. the research further suggests that a third country should observe the voting system adopted for a particular case by the EU in order to form a better understanding of the EU's possible policy outcomes.