The ‘Wallonian Saga’ associated with the threat on behalf of the Wallonian regional government to block the signature of the Comprehensive Economic and Trade Agreement (CETA) in October 2016 has illustrated a number of structural weaknesses of the European Union as an external treaty-maker in the field of EU Common Commercial Policy. These weaknesses concern issues of both democratic representation and the effectiveness of EU multilevel governance. The legal question of competence that determines the Union’s power to conclude external commercial treaties by itself or, in the alternative, jointly with the Member States has now been clarified by the CJEU in Opinion 2/15. Against this backdrop, this article examines and discusses the constitutional fundamentals of EU economic treaty-making. The article provides an explanatory account of the division and nature of treaty-making competences in the EU; outlines the distinct modalities and procedures that the conclusion of international treaties as ‘EU-only’ or ‘mixed’ require respectively; discusses the law and practice of the provisional application of international economic treaties by the EU; reviews legal avenues that enable the entry into force of a mixed agreement despite its rejection by an individual Member State; and gives an overview of the relevant CJEU case law and the Court’s conclusions in Opinion 2/15. Normatively, we argue in favour of adjusting the scope of future EU trade and investment agreements to the realm of EU exclusive competences in order to remedy the functional deficiencies of EU treaty-making that were exposed in the ‘CETA-drama’. At the same time, we emphasize the need for – and outline a path towards – a qualitative change in EU and Member State institutional practice that fully employs the channels of vertical political participation in the Union’s multilevel governance structures so as to strengthen the legitimacy of EU economic treaty-making.