Existing scholarly and policy approaches to the EU’s ‘neighbourhood’ have been criticized for being excessively Euro-centric, for geopoliticizing and securitizing relations with third countries, and for being generally ineffective. With this Introduction, we contend that relational theories can offer a less asymmetrical and biased understanding of the interactions between the EU and its borderlands. Relationality posits that outcomes in international relations are socially situated and that co-constitutive relations can shape actors and their actions even more profoundly than their material capabilities or structural constraints. The proposed framework thus focuses on the relations, practices and patterns of cooperation occurring at different levels of governance (vertical and horizontal) in and around Europe’s borderlands. Vertical governance refers here to the interactions occurring at various levels within the EU – between EU institutions and member states as well as within institutions themselves – that shape the Union’s policies to the East and South. Horizonal governance, instead, refers to the interactions between systems of governance across borders (e.g., between the EU and a third country’s government, as well as non-state actors). In an attempt to de-centre our conceptualization of the Union’s borderlands while offering a holistic picture, we apply this framework from the perspective of the EU’s borderlands looking in and from that of the EU looking out.