Geopolitical and security dynamics are shifting in the Indo-Pacific as states across the region adjust to China’s growing influence and the era of great-power competition between the United States and China. These geopolitical shifts are also intersecting with the accelerating rate of innovation in technologies associated with the Fourth Industrial Revolution (4IR) to reshape the future of military-technological competition and emerging military operations. This report, Emerging Technologies and the Future of US-Japan Defense Collaboration, by Tate Nurkin and Ryo Hinata-Yamaguchi, explores the drivers, tensions, and constraints shaping US-Japan collaboration on emerging defense technologies while providing concrete recommendations for the US-Japan alliance to accelerate and intensify long-standing military and defense-focused coordination and collaboration.