This article takes the move from the recognition that the law of EU external relations is fragmentary. EU foreign affairs are conducted through a Common Foreign and Security Policy (CFSP), a Common Commercial Policy, and other competences with external implications. This article is dedicated to one of such competences, whose external side has been hitherto largely underexplored: the monetary policy of Member States whose currency is the Euro. With a view of offering a first assessment of this ‘banking diplomacy’ law, the article outlines the main legal features of the external aspects of Banking Union (BU) and their interactions with other external relations competences. It does so by following four themes: investment, external representation, prudential supervision, and resolution.