<p>This article examines the evolving EU-Japan security cooperation in the context of the deteriorating global security environment over the past decade with a focus on EU-Japanese efforts in upholding the Liberal International Order (LIO). Conceptually, the article builds on both partners’ vested interests and strong attachment to the LIO, and the rules and norms that underpin it, including the rule of law, multilateralism, and free trade. Concretely, it argues that the multiple security challenges that have emerged in the context of the contested LIO, namely great power competition and the relative decline of the USA, the rise of authoritarian regimes, and the emergence of hybrid threats, constitute a powerful driver for strengthening EU-Japan security cooperation. Within the security realm, maritime security, and cybersecurity and digital connectivity, as well as defence technology cooperation have been particularly important areas for the two partners in responding to the challenges to the LIO. The article also demonstrates that EU-Japanese joint responses in upholding the LIO face important constraints. Therefore, the future of the bilateral security cooperation will depend in many ways on both partners’ careful assessment of respective strategic priorities, resources, and limitations.</p>