The European Union represents a unique form of cooperation, and become a major player, given the fact that its foreign policy has an impact on the international architecture. Some of the ambiguity of this phenomenon by means of the interpretation in terms of several research methods is analyzed. Moreover, the main coordinates of the development of the European Security and Defencе Policy are examined, in the framework of expressions of national security interests of the EU Member States, especially Romania. In order to understand the genesis and evolution of the European security and European defence policy, as well as the relations between the European Union and Romania, are addressed two additional methodological practices: the objective, based on the concept of epistemological explanations, and the interpretive practice based on the epistemological concepts of understanding and interpretation. Romania has consistently advocated for the improvement and promotion of its national interests, effectively using the tools of its national diplomatic, economic, military and information power. Active participation of Romania in achieving the objectives of the European Security and Defence Policy (ESDP), transformed into the Common Security and Defence Policy (CSDP), brings both advantages and new responsibilities in the field of security.