This chapter explores Japan’s ARF policy with reference to the process of preventive diplomacy (PD). This chapter begins by providing a brief review of regional discussion on the concept and measures of PD at the Track Two level in the first years after the establishment of the ARF in order to explain the origin and meaning of PD. The second section examines both Japan’s and China’s views of the concept and measures of PD and contrasts them with each other. The third section looks at Japan’s actual diplomacy in the PD agenda in the ARF. Japan’s experience in this area has demonstrated that the Forum has encountered grave difficulties in developing practical PD mechanisms and that its potential to play a meaningful PD role has so far remained highly limited.