In general I am interested in the interplay between international relations and energy. This is a growing field of research and I aim through my thesis to contribute to its development. The objective is to gain an in-depth understanding of the energy issues that affect international politics. In particular, the EU as an institution is deeply concerned for the security of its energy supply. Although it attempts to act as a unified actor within the regional and international framework, the energy security considerations of its member states force some of them to act individually. Therefore, I test: a) how international relations theory is developed concentrating mainly in the neo-realism neo-liberalism debate, and, b) how energy and national security interact with a special interest on the case of Greece.