The Principle of Sincere Cooperation in EU External Relations Law

Sincere cooperation has become a pivotal principle in the field of EU external relations law. Enshrined in article 4(3) TEU, the principle of sincere cooperation establishes reciprocal duties of assistance between the Union and the Member States as well as positive and negative obligations resting on the Member States to enable the Union to achieve its tasks and objectives. As a derivative non-unitary actor, the Union shares the international scene with its Member States and it is this coexistence that, more than in the internal field, challenges the unity and coherence of Union action. The present thesis focuses on the principle sincere cooperation and aims to investigate the contribution of the principle to the exercise of the Union’s external competences when it concludes international agreements and to the subsequent compliance with those agreements within the EU legal order. In this way, the thesis will consider how the external dimension of the principle influences the EU’s action on the international plane and the relationship between international and European law within the EU legal order.