"Reducing health disparity" is one of the basic goals in the revised notice of "Basic Plans to Comprehensively Promote Citizen's Health" (Health Japan 21 (2^nd edition)) by the Ministry of Health, Labor and Welfare. The revision is based on the re-recognition of the importance of social determinants of health (SDHs). This paper focuses on health disparities and their social determinants, and discusses their implication for Health Economics and Policy research from various perspectives.

First, SDHs have been and will be identified as an important research topic in Health Economics and Policy. Second, an increased focus on SDHs in health policy debate resulted from prevailing recognition of limited efficacy of previous health educational interventions to modify individual behaviors, as the final evaluations of "Health Japan 21 (1^st edition)" also concluded. Furthermore widening socioeconomic inequality pushes many countries to already start policy initiatives on SDHs. and Japan is about to follow this global trend.

Third, I propose that health economics and policy research on SDHs requires a tri-pod framework; 1) an ecological perspective that involves individuals, communities, and national governments, 2) a process perspective that addresses social diagnosis, causal complex mechanism, and translation into policy countermeasure, and 3) a life-course perspective.

Fourth, it is necessary to immediately take an action to reduce health disparities, and health economics and policy should play a due role. Other countries have spent more than 10 years to develop comprehensive policies, and the contributions by health economics are not ignorable in providing concepts, measurement, theoretical frame, and econometric models for sophisticated causal inference. Furthermore, a few examples of how to overcome issues related to policy science are mentioned.

To conclude the paper, I strongly argue that it is possible to reduce health disparity. If we fail to take immediate actions, health disparity is expected to worsen due to growing poverty and unstable employment; however, we can undertake measures to reduce it.