The European Union (EU) and Taiwan (officially the Republic of China) are both non-conventional polities in international relations and the study of diplomacy. On the one hand, the EU is a ‘unique economic and political union between 27 European countries’. On the other hand, Taiwan is able to concurrently carry out two distinct forms of foreign relations. First, diplomacy as a sovereign country with states that it maintains formal diplomatic relations. Second, in the relations with states and other polities without diplomatic ties, and under their divergent ‘One China’ policies, Taiwan operates as a paradiplomatic actor or one that is within the intervals of diplomacy and paradiplomacy. Observing such a phenomenon, this article proposes the notion of ‘amphibious diplomacy’ and empirically studies the notion through how, in practice, the EU and Taiwan have been carrying out their negotiation of the Bilateral Investment Agreement ( bia ) given the constraints of an absence of diplomatic relations and the EU’s ‘One China’ policy. The article incorporates first-hand material from semi-structured interviews with interlocutors whose work allows them to obtain practical knowledge about the EU-Taiwan bia .