This book explores the role of the European Union (EU) in the cooperation and regulation of the Baltic Sea Region (BSR), from both an institutional and substantive perspective. It particularly focuses on the role of the Union in advancing the broader marine governance framework in the region. Questions investigated include: in what way does the Union participate in, or otherwise influence, the activities of States, international organisations and other actors involved in BSR cooperation and regulation, and what is the importance and substantive outcome of the Union's specific role in this respect? How has the membership of eight out of nine Baltic Sea coastal States in the EU affected cooperation in the region, in terms of substance as well as procedure, and what is the influence of the BSR over the EU? These questions are discussed from different perspectives by leading experts in both the fields of EU law and the law of the BSR.