This article presents three main arguments: First, shared competence exists between the national and supranational levels within the European Union (EU) because EU Member States do not trust the European Commission in the external relations law of the EU. Second, the EU will have greater bargaining power in international negotiations if it speaks in a single voice. Within the EU-27, we have compatible values, overlapping interests, shared goals, as well as economic, social and political ties. Therefore, there is a presumption of collective action in the EU’s external relations. However, EU Member States disagree on many issues before they start negotiations, while trying to define a mission together as partners of the European project. Third, Member States confer specific negotiating powers on the EU only when it is in their own national interest to have a common European position on international negotiations.