The article elaborates on the significance of the duty of sincere cooperation as a legal principle in the Common Commercial Policy (CCP) of the European Union (EU), in particular as regards the relationship between the Union and its Member States. It argues that while the duty of sincere cooperation is a judicially enforceable duty vis-a-vis the Member States, it is losing some of its relevance in the context of the CCP. This is due to the fact that the Lisbon Treaty, as confirmed by the case law of the Court of Justice of the EU, expanded the scope of the CCP and clearly identifies it as an exclusive competence of the Union. Loyalty in the CCP, therefore, is mainly covered by the obligation to respect the exclusivity of the Union's international powers in this area. While this does not equate to the disappearance of the Member States as actors in international economic governance, it does seriously constrain their leeway for autonomous action. In addition, the article applies this finding to a number of current developments surrounding the CCP. These include, firstly, the new Global Strategy for Foreign and Security Policy, which promotes the idea of a "joined-up" approach between different actors and policies; secondly, "Brexit" and the prospect of the United Kingdom negotiating new trade agreements of its own; thirdly, the position of the Member States in the WTO; and fourthly, the nature of the wave of new free trade agreements that the EU is negotiating and concluding.