Ass. Prof. Dr. Todor Kolarov 
The article discusses different manifestations of the duty to cooperate in EU external relations. It starts with some preliminary remarks on the meaning of the notions “duty to cooperate” and “loyal cooperation” and the difference between them. It explains that “loyal cooperation” is demonstration of the “duty to cooperate”.
Further in the article, these manifestations of the duty to cooperate are classified according to different criteria. Under this rubric the article discusses the well-known impossibility of MS to exercise their external competence due to the EU exercising its internal competence. However, it also attributes attention to the impossibility of MS to exercise their external competence due to the possibility of affecting the competence of the EU. Further, the substantive and procedural dimensions of the duty to cooperate and the classification of the duty to cooperate as a duty to deliver a result or to follow a procedure without necessarily delivering results are part of the classification. Another criterion is whether the prerequisites for the duty to cooperate are set in a legislative or constitutional source of EU law. The phase in which the duty to cooperate is demonstrated and the moment in which the duty materializes is also discussed. An important classification is whether the duty falls on the MS or EU and whether it is a duty to act or refrain from action. Finally, attention is attributed to the dimensions of the duty to cooperate with respect to agreements concluded prior to accession to the EU.
In its final part, the piece draws conclusions on the scope of the duty to cooperate in EU external relations. Although the duty to cooperate is a duty that applies to both MS and EU, the practice of the Court of Justice of the EU seems to impose a higher standard of the obligation on the MS.
За достъп до пълната версия на статията, следвайте този линк: Задължението за сътрудничество и ефекта му върху компетентността при смесените договори на ЕС
 Associate Professor at the New Bulgarian University and Adjunct Associate Professor at the American University in Bulgaria. Member of the Arbitration Council of the Arbitration Court of the Confederation of Bulgarian Employers and Industrialists. Consultant for the UNODC and EU. Previously, Todor Kolarov served as the chairperson of the Bulgarian criminal asset confiscation body. His publications are mainly in the field of freezing and confiscation of criminal assets.