This chapter addresses non-proliferation as an agenda item in EU–Japan cooperation. For both sides, how to prevent proliferation, not just of Weapons of Mass Destruction (WMD) like nuclear weapons, but also of their delivery vehicles and other sensitive technologies, has always been a problem of high priority. The chapter examines the levels of threat perceptions on proliferation in the EU and Japan respectively, then explores policy responses by the EU and Japan to the problems of proliferation including arms export and export control. Finally, the chapter examines EU–Japan cooperation so far and prospects for such cooperation both in the bilateral and multilateral contexts. The level of EU–Japan cooperation in non-proliferation is not as high as it could be given the high level of commitment the two partners have to the issue. However, there is more potential, including in the areas of nuclear security, container security and export control.